node_modules

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diff --git a/node_modules/selenium-webdriver/lib/webdriver.js b/node_modules/selenium-webdriver/lib/webdriver.js
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+++ b/node_modules/selenium-webdriver/lib/webdriver.js
@@ -0,0 +1,2459 @@
+// Licensed to the Software Freedom Conservancy (SFC) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The SFC licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+/**
+ * @fileoverview The heart of the WebDriver JavaScript API.
+ */
+
+'use strict';
+
+const actions = require('./actions');
+const by = require('./by');
+const Capabilities = require('./capabilities').Capabilities;
+const command = require('./command');
+const error = require('./error');
+const input = require('./input');
+const logging = require('./logging');
+const Session = require('./session').Session;
+const Symbols = require('./symbols');
+const promise = require('./promise');
+
+
+/**
+ * Defines a condition for use with WebDriver's {@linkplain WebDriver#wait wait
+ * command}.
+ *
+ * @template OUT
+ */
+class Condition {
+  /**
+   * @param {string} message A descriptive error message. Should complete the
+   *     sentence "Waiting [...]"
+   * @param {function(!WebDriver): OUT} fn The condition function to
+   *     evaluate on each iteration of the wait loop.
+   */
+  constructor(message, fn) {
+    /** @private {string} */
+    this.description_ = 'Waiting ' + message;
+
+    /** @type {function(!WebDriver): OUT} */
+    this.fn = fn;
+  }
+
+  /** @return {string} A description of this condition. */
+  description() {
+    return this.description_;
+  }
+}
+
+
+/**
+ * Defines a condition that will result in a {@link WebElement}.
+ *
+ * @extends {Condition<!(WebElement|promise.Promise<!WebElement>)>}
+ */
+class WebElementCondition extends Condition {
+  /**
+   * @param {string} message A descriptive error message. Should complete the
+   *     sentence "Waiting [...]"
+   * @param {function(!WebDriver): !(WebElement|promise.Promise<!WebElement>)}
+   *     fn The condition function to evaluate on each iteration of the wait
+   *     loop.
+   */
+  constructor(message, fn) {
+    super(message, fn);
+  }
+}
+
+
+//////////////////////////////////////////////////////////////////////////////
+//
+//  WebDriver
+//
+//////////////////////////////////////////////////////////////////////////////
+
+
+/**
+ * Translates a command to its wire-protocol representation before passing it
+ * to the given `executor` for execution.
+ * @param {!command.Executor} executor The executor to use.
+ * @param {!command.Command} command The command to execute.
+ * @return {!Promise} A promise that will resolve with the command response.
+ */
+function executeCommand(executor, command) {
+  return toWireValue(command.getParameters()).
+      then(function(parameters) {
+        command.setParameters(parameters);
+        return executor.execute(command);
+      });
+}
+
+
+/**
+ * Converts an object to its JSON representation in the WebDriver wire protocol.
+ * When converting values of type object, the following steps will be taken:
+ * <ol>
+ * <li>if the object is a WebElement, the return value will be the element's
+ *     server ID
+ * <li>if the object defines a {@link Symbols.serialize} method, this algorithm
+ *     will be recursively applied to the object's serialized representation
+ * <li>if the object provides a "toJSON" function, this algorithm will
+ *     recursively be applied to the result of that function
+ * <li>otherwise, the value of each key will be recursively converted according
+ *     to the rules above.
+ * </ol>
+ *
+ * @param {*} obj The object to convert.
+ * @return {!Promise<?>} A promise that will resolve to the input value's JSON
+ *     representation.
+ */
+function toWireValue(obj) {
+  if (promise.isPromise(obj)) {
+    return Promise.resolve(obj).then(toWireValue);
+  }
+  return Promise.resolve(convertValue(obj));
+}
+
+
+function convertValue(value) {
+  if (value === void 0 || value === null) {
+    return value;
+  }
+
+  if (typeof value === 'boolean'
+      || typeof value === 'number'
+      || typeof value === 'string') {
+    return value;
+  }
+
+  if (Array.isArray(value)) {
+    return convertKeys(value);
+  }
+
+  if (typeof value === 'function') {
+    return '' + value;
+  }
+
+  if (typeof value[Symbols.serialize] === 'function') {
+    return toWireValue(value[Symbols.serialize]());
+  } else if (typeof value.toJSON === 'function') {
+    return toWireValue(value.toJSON());
+  }
+  return convertKeys(value);
+}
+
+
+function convertKeys(obj) {
+  const isArray = Array.isArray(obj);
+  const numKeys = isArray ? obj.length : Object.keys(obj).length;
+  const ret = isArray ? new Array(numKeys) : {};
+  if (!numKeys) {
+    return Promise.resolve(ret);
+  }
+
+  let numResolved = 0;
+
+  function forEachKey(obj, fn) {
+    if (Array.isArray(obj)) {
+      for (let i = 0, n = obj.length; i < n; i++) {
+        fn(obj[i], i);
+      }
+    } else {
+      for (let key in obj) {
+        fn(obj[key], key);
+      }
+    }
+  }
+
+  return new Promise(function(done, reject) {
+    forEachKey(obj, function(value, key) {
+      if (promise.isPromise(value)) {
+        value.then(toWireValue).then(setValue, reject);
+      } else {
+        value = convertValue(value);
+        if (promise.isPromise(value)) {
+          value.then(toWireValue).then(setValue, reject);
+        } else {
+          setValue(value);
+        }
+      }
+
+      function setValue(value) {
+        ret[key] = value;
+        maybeFulfill();
+      }
+    });
+
+    function maybeFulfill() {
+      if (++numResolved === numKeys) {
+        done(ret);
+      }
+    }
+  });
+}
+
+
+/**
+ * Converts a value from its JSON representation according to the WebDriver wire
+ * protocol. Any JSON object that defines a WebElement ID will be decoded to a
+ * {@link WebElement} object. All other values will be passed through as is.
+ *
+ * @param {!WebDriver} driver The driver to use as the parent of any unwrapped
+ *     {@link WebElement} values.
+ * @param {*} value The value to convert.
+ * @return {*} The converted value.
+ */
+function fromWireValue(driver, value) {
+  if (Array.isArray(value)) {
+    value = value.map(v => fromWireValue(driver, v));
+  } else if (WebElement.isId(value)) {
+    let id = WebElement.extractId(value);
+    value = new WebElement(driver, id);
+  } else if (value && typeof value === 'object') {
+    let result = {};
+    for (let key in value) {
+      if (value.hasOwnProperty(key)) {
+        result[key] = fromWireValue(driver, value[key]);
+      }
+    }
+    value = result;
+  }
+  return value;
+}
+
+
+/**
+ * Creates a new WebDriver client, which provides control over a browser.
+ *
+ * Every command.Command returns a {@link promise.Promise} that
+ * represents the result of that command. Callbacks may be registered on this
+ * object to manipulate the command result or catch an expected error. Any
+ * commands scheduled with a callback are considered sub-commands and will
+ * execute before the next command in the current frame. For example:
+ *
+ *     var message = [];
+ *     driver.call(message.push, message, 'a').then(function() {
+ *       driver.call(message.push, message, 'b');
+ *     });
+ *     driver.call(message.push, message, 'c');
+ *     driver.call(function() {
+ *       alert('message is abc? ' + (message.join('') == 'abc'));
+ *     });
+ *
+ */
+class WebDriver {
+  /**
+   * @param {!(Session|promise.Promise<!Session>)} session Either a
+   *     known session or a promise that will be resolved to a session.
+   * @param {!command.Executor} executor The executor to use when sending
+   *     commands to the browser.
+   * @param {promise.ControlFlow=} opt_flow The flow to
+   *     schedule commands through. Defaults to the active flow object.
+   */
+  constructor(session, executor, opt_flow) {
+    /** @private {!promise.Promise<!Session>} */
+    this.session_ = promise.fulfilled(session);
+
+    /** @private {!command.Executor} */
+    this.executor_ = executor;
+
+    /** @private {!promise.ControlFlow} */
+    this.flow_ = opt_flow || promise.controlFlow();
+
+    /** @private {input.FileDetector} */
+    this.fileDetector_ = null;
+  }
+
+  /**
+   * Creates a new WebDriver client for an existing session.
+   * @param {!command.Executor} executor Command executor to use when querying
+   *     for session details.
+   * @param {string} sessionId ID of the session to attach to.
+   * @param {promise.ControlFlow=} opt_flow The control flow all
+   *     driver commands should execute under. Defaults to the
+   *     {@link promise.controlFlow() currently active}  control flow.
+   * @return {!WebDriver} A new client for the specified session.
+   */
+  static attachToSession(executor, sessionId, opt_flow) {
+    let flow = opt_flow || promise.controlFlow();
+    let cmd = new command.Command(command.Name.DESCRIBE_SESSION)
+        .setParameter('sessionId', sessionId);
+    let session = flow.execute(
+        () => executeCommand(executor, cmd).catch(err => {
+          // The DESCRIBE_SESSION command is not supported by the W3C spec, so
+          // if we get back an unknown command, just return a session with
+          // unknown capabilities.
+          if (err instanceof error.UnknownCommandError) {
+            return new Session(sessionId, new Capabilities);
+          }
+          throw err;
+        }),
+        'WebDriver.attachToSession()');
+    return new WebDriver(session, executor, flow);
+  }
+
+  /**
+   * Creates a new WebDriver session.
+   *
+   * By default, the requested session `capabilities` are merely "desired" and
+   * the remote end will still create a new session even if it cannot satisfy
+   * all of the requested capabilities. You can query which capabilities a
+   * session actually has using the
+   * {@linkplain #getCapabilities() getCapabilities()} method on the returned
+   * WebDriver instance.
+   *
+   * To define _required capabilities_, provide the `capabilities` as an object
+   * literal with `required` and `desired` keys. The `desired` key may be
+   * omitted if all capabilities are required, and vice versa. If the server
+   * cannot create a session with all of the required capabilities, it will
+   * return an {@linkplain error.SessionNotCreatedError}.
+   *
+   *     let required = new Capabilities().set('browserName', 'firefox');
+   *     let desired = new Capabilities().set('version', '45');
+   *     let driver = WebDriver.createSession(executor, {required, desired});
+   *
+   * This function will always return a WebDriver instance. If there is an error
+   * creating the session, such as the aforementioned SessionNotCreatedError,
+   * the driver will have a rejected {@linkplain #getSession session} promise.
+   * It is recommended that this promise is left _unhandled_ so it will
+   * propagate through the {@linkplain promise.ControlFlow control flow} and
+   * cause subsequent commands to fail.
+   *
+   *     let required = Capabilities.firefox();
+   *     let driver = WebDriver.createSession(executor, {required});
+   *
+   *     // If the createSession operation failed, then this command will also
+   *     // also fail, propagating the creation failure.
+   *     driver.get('http://www.google.com').catch(e => console.log(e));
+   *
+   * @param {!command.Executor} executor The executor to create the new session
+   *     with.
+   * @param {(!Capabilities|
+   *          {desired: (Capabilities|undefined),
+   *           required: (Capabilities|undefined)})} capabilities The desired
+   *     capabilities for the new session.
+   * @param {promise.ControlFlow=} opt_flow The control flow all driver
+   *     commands should execute under, including the initial session creation.
+   *     Defaults to the {@link promise.controlFlow() currently active}
+   *     control flow.
+   * @return {!WebDriver} The driver for the newly created session.
+   */
+  static createSession(executor, capabilities, opt_flow) {
+    let flow = opt_flow || promise.controlFlow();
+    let cmd = new command.Command(command.Name.NEW_SESSION);
+
+    if (capabilities && (capabilities.desired || capabilities.required)) {
+      cmd.setParameter('desiredCapabilities', capabilities.desired);
+      cmd.setParameter('requiredCapabilities', capabilities.required);
+    } else {
+      cmd.setParameter('desiredCapabilities', capabilities);
+    }
+
+    let session = flow.execute(
+        () => executeCommand(executor, cmd),
+        'WebDriver.createSession()');
+    return new WebDriver(session, executor, flow);
+  }
+
+  /**
+   * @return {!promise.ControlFlow} The control flow used by this
+   *     instance.
+   */
+  controlFlow() {
+    return this.flow_;
+  }
+
+  /**
+   * Schedules a {@link command.Command} to be executed by this driver's
+   * {@link command.Executor}.
+   *
+   * @param {!command.Command} command The command to schedule.
+   * @param {string} description A description of the command for debugging.
+   * @return {!promise.Promise<T>} A promise that will be resolved
+   *     with the command result.
+   * @template T
+   */
+  schedule(command, description) {
+    var self = this;
+
+    checkHasNotQuit();
+    command.setParameter('sessionId', this.session_);
+
+    // If any of the command parameters are rejected promises, those
+    // rejections may be reported as unhandled before the control flow
+    // attempts to execute the command. To ensure parameters errors
+    // propagate through the command itself, we resolve all of the
+    // command parameters now, but suppress any errors until the ControlFlow
+    // actually executes the command. This addresses scenarios like catching
+    // an element not found error in:
+    //
+    //     driver.findElement(By.id('foo')).click().catch(function(e) {
+    //       if (e instanceof NoSuchElementError) {
+    //         // Do something.
+    //       }
+    //     });
+    var prepCommand = toWireValue(command.getParameters());
+    prepCommand.catch(function() {});
+
+    var flow = this.flow_;
+    var executor = this.executor_;
+    return flow.execute(function() {
+      // A call to WebDriver.quit() may have been scheduled in the same event
+      // loop as this |command|, which would prevent us from detecting that the
+      // driver has quit above.  Therefore, we need to make another quick check.
+      // We still check above so we can fail as early as possible.
+      checkHasNotQuit();
+
+      // Retrieve resolved command parameters; any previously suppressed errors
+      // will now propagate up through the control flow as part of the command
+      // execution.
+      return prepCommand.then(function(parameters) {
+        command.setParameters(parameters);
+        return executor.execute(command);
+      }).then(value => fromWireValue(self, value));
+    }, description);
+
+    function checkHasNotQuit() {
+      if (!self.session_) {
+        throw new error.NoSuchSessionError(
+          'This driver instance does not have a valid session ID ' +
+          '(did you call WebDriver.quit()?) and may no longer be ' +
+          'used.');
+      }
+    }
+  }
+
+  /**
+   * Sets the {@linkplain input.FileDetector file detector} that should be
+   * used with this instance.
+   * @param {input.FileDetector} detector The detector to use or {@code null}.
+   */
+  setFileDetector(detector) {
+    this.fileDetector_ = detector;
+  }
+
+  /**
+   * @return {!command.Executor} The command executor used by this instance.
+   */
+  getExecutor() {
+    return this.executor_;
+  }
+
+  /**
+   * @return {!promise.Promise<!Session>} A promise for this client's
+   *     session.
+   */
+  getSession() {
+    return this.session_;
+  }
+
+  /**
+   * @return {!promise.Promise<!Capabilities>} A promise
+   *     that will resolve with the this instance's capabilities.
+   */
+  getCapabilities() {
+    return this.session_.then(session => session.getCapabilities());
+  }
+
+  /**
+   * Schedules a command to quit the current session. After calling quit, this
+   * instance will be invalidated and may no longer be used to issue commands
+   * against the browser.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the command has completed.
+   */
+  quit() {
+    var result = this.schedule(
+        new command.Command(command.Name.QUIT),
+        'WebDriver.quit()');
+    // Delete our session ID when the quit command finishes; this will allow us
+    // to throw an error when attemnpting to use a driver post-quit.
+    return result.finally(() => delete this.session_);
+  }
+
+  /**
+   * Creates a new action sequence using this driver. The sequence will not be
+   * scheduled for execution until {@link actions.ActionSequence#perform} is
+   * called. Example:
+   *
+   *     driver.actions().
+   *         mouseDown(element1).
+   *         mouseMove(element2).
+   *         mouseUp().
+   *         perform();
+   *
+   * @return {!actions.ActionSequence} A new action sequence for this instance.
+   */
+  actions() {
+    return new actions.ActionSequence(this);
+  }
+
+  /**
+   * Creates a new touch sequence using this driver. The sequence will not be
+   * scheduled for execution until {@link actions.TouchSequence#perform} is
+   * called. Example:
+   *
+   *     driver.touchActions().
+   *         tap(element1).
+   *         doubleTap(element2).
+   *         perform();
+   *
+   * @return {!actions.TouchSequence} A new touch sequence for this instance.
+   */
+  touchActions() {
+    return new actions.TouchSequence(this);
+  }
+
+  /**
+   * Schedules a command to execute JavaScript in the context of the currently
+   * selected frame or window. The script fragment will be executed as the body
+   * of an anonymous function. If the script is provided as a function object,
+   * that function will be converted to a string for injection into the target
+   * window.
+   *
+   * Any arguments provided in addition to the script will be included as script
+   * arguments and may be referenced using the {@code arguments} object.
+   * Arguments may be a boolean, number, string, or {@linkplain WebElement}.
+   * Arrays and objects may also be used as script arguments as long as each item
+   * adheres to the types previously mentioned.
+   *
+   * The script may refer to any variables accessible from the current window.
+   * Furthermore, the script will execute in the window's context, thus
+   * {@code document} may be used to refer to the current document. Any local
+   * variables will not be available once the script has finished executing,
+   * though global variables will persist.
+   *
+   * If the script has a return value (i.e. if the script contains a return
+   * statement), then the following steps will be taken for resolving this
+   * functions return value:
+   *
+   * - For a HTML element, the value will resolve to a {@linkplain WebElement}
+   * - Null and undefined return values will resolve to null</li>
+   * - Booleans, numbers, and strings will resolve as is</li>
+   * - Functions will resolve to their string representation</li>
+   * - For arrays and objects, each member item will be converted according to
+   *     the rules above
+   *
+   * @param {!(string|Function)} script The script to execute.
+   * @param {...*} var_args The arguments to pass to the script.
+   * @return {!promise.Promise<T>} A promise that will resolve to the
+   *    scripts return value.
+   * @template T
+   */
+  executeScript(script, var_args) {
+    if (typeof script === 'function') {
+      script = 'return (' + script + ').apply(null, arguments);';
+    }
+    let args =
+        arguments.length > 1 ? Array.prototype.slice.call(arguments, 1) : [];
+   return this.schedule(
+        new command.Command(command.Name.EXECUTE_SCRIPT).
+            setParameter('script', script).
+            setParameter('args', args),
+        'WebDriver.executeScript()');
+  }
+
+  /**
+   * Schedules a command to execute asynchronous JavaScript in the context of the
+   * currently selected frame or window. The script fragment will be executed as
+   * the body of an anonymous function. If the script is provided as a function
+   * object, that function will be converted to a string for injection into the
+   * target window.
+   *
+   * Any arguments provided in addition to the script will be included as script
+   * arguments and may be referenced using the {@code arguments} object.
+   * Arguments may be a boolean, number, string, or {@code WebElement}.
+   * Arrays and objects may also be used as script arguments as long as each item
+   * adheres to the types previously mentioned.
+   *
+   * Unlike executing synchronous JavaScript with {@link #executeScript},
+   * scripts executed with this function must explicitly signal they are finished
+   * by invoking the provided callback. This callback will always be injected
+   * into the executed function as the last argument, and thus may be referenced
+   * with {@code arguments[arguments.length - 1]}. The following steps will be
+   * taken for resolving this functions return value against the first argument
+   * to the script's callback function:
+   *
+   * - For a HTML element, the value will resolve to a
+   *     {@link WebElement}
+   * - Null and undefined return values will resolve to null
+   * - Booleans, numbers, and strings will resolve as is
+   * - Functions will resolve to their string representation
+   * - For arrays and objects, each member item will be converted according to
+   *     the rules above
+   *
+   * __Example #1:__ Performing a sleep that is synchronized with the currently
+   * selected window:
+   *
+   *     var start = new Date().getTime();
+   *     driver.executeAsyncScript(
+   *         'window.setTimeout(arguments[arguments.length - 1], 500);').
+   *         then(function() {
+   *           console.log(
+   *               'Elapsed time: ' + (new Date().getTime() - start) + ' ms');
+   *         });
+   *
+   * __Example #2:__ Synchronizing a test with an AJAX application:
+   *
+   *     var button = driver.findElement(By.id('compose-button'));
+   *     button.click();
+   *     driver.executeAsyncScript(
+   *         'var callback = arguments[arguments.length - 1];' +
+   *         'mailClient.getComposeWindowWidget().onload(callback);');
+   *     driver.switchTo().frame('composeWidget');
+   *     driver.findElement(By.id('to')).sendKeys('dog@example.com');
+   *
+   * __Example #3:__ Injecting a XMLHttpRequest and waiting for the result. In
+   * this example, the inject script is specified with a function literal. When
+   * using this format, the function is converted to a string for injection, so it
+   * should not reference any symbols not defined in the scope of the page under
+   * test.
+   *
+   *     driver.executeAsyncScript(function() {
+   *       var callback = arguments[arguments.length - 1];
+   *       var xhr = new XMLHttpRequest();
+   *       xhr.open("GET", "/resource/data.json", true);
+   *       xhr.onreadystatechange = function() {
+   *         if (xhr.readyState == 4) {
+   *           callback(xhr.responseText);
+   *         }
+   *       };
+   *       xhr.send('');
+   *     }).then(function(str) {
+   *       console.log(JSON.parse(str)['food']);
+   *     });
+   *
+   * @param {!(string|Function)} script The script to execute.
+   * @param {...*} var_args The arguments to pass to the script.
+   * @return {!promise.Promise<T>} A promise that will resolve to the
+   *    scripts return value.
+   * @template T
+   */
+  executeAsyncScript(script, var_args) {
+    if (typeof script === 'function') {
+      script = 'return (' + script + ').apply(null, arguments);';
+    }
+    let args = Array.prototype.slice.call(arguments, 1);
+    return this.schedule(
+        new command.Command(command.Name.EXECUTE_ASYNC_SCRIPT).
+            setParameter('script', script).
+            setParameter('args', args),
+        'WebDriver.executeScript()');
+  }
+
+  /**
+   * Schedules a command to execute a custom function.
+   * @param {function(...): (T|promise.Promise<T>)} fn The function to
+   *     execute.
+   * @param {Object=} opt_scope The object in whose scope to execute the function.
+   * @param {...*} var_args Any arguments to pass to the function.
+   * @return {!promise.Promise<T>} A promise that will be resolved'
+   *     with the function's result.
+   * @template T
+   */
+  call(fn, opt_scope, var_args) {
+    let args = Array.prototype.slice.call(arguments, 2);
+    let flow = this.flow_;
+    return flow.execute(function() {
+      return promise.fullyResolved(args).then(function(args) {
+        if (promise.isGenerator(fn)) {
+          args.unshift(fn, opt_scope);
+          return promise.consume.apply(null, args);
+        }
+        return fn.apply(opt_scope, args);
+      });
+    }, 'WebDriver.call(' + (fn.name || 'function') + ')');
+  }
+
+  /**
+   * Schedules a command to wait for a condition to hold. The condition may be
+   * specified by a {@link Condition}, as a custom function, or as any
+   * promise-like thenable.
+   *
+   * For a {@link Condition} or function, the wait will repeatedly
+   * evaluate the condition until it returns a truthy value. If any errors occur
+   * while evaluating the condition, they will be allowed to propagate. In the
+   * event a condition returns a {@link promise.Promise promise}, the polling
+   * loop will wait for it to be resolved and use the resolved value for whether
+   * the condition has been satisified. Note the resolution time for a promise
+   * is factored into whether a wait has timed out.
+   *
+   * Note, if the provided condition is a {@link WebElementCondition}, then
+   * the wait will return a {@link WebElementPromise} that will resolve to the
+   * element that satisified the condition.
+   *
+   * _Example:_ waiting up to 10 seconds for an element to be present on the
+   * page.
+   *
+   *     var button = driver.wait(until.elementLocated(By.id('foo')), 10000);
+   *     button.click();
+   *
+   * This function may also be used to block the command flow on the resolution
+   * of any thenable promise object. When given a promise, the command will
+   * simply wait for its resolution before completing. A timeout may be provided
+   * to fail the command if the promise does not resolve before the timeout
+   * expires.
+   *
+   * _Example:_ Suppose you have a function, `startTestServer`, that returns a
+   * promise for when a server is ready for requests. You can block a WebDriver
+   * client on this promise with:
+   *
+   *     var started = startTestServer();
+   *     driver.wait(started, 5 * 1000, 'Server should start within 5 seconds');
+   *     driver.get(getServerUrl());
+   *
+   * @param {!(promise.Promise<T>|
+   *           Condition<T>|
+   *           function(!WebDriver): T)} condition The condition to
+   *     wait on, defined as a promise, condition object, or  a function to
+   *     evaluate as a condition.
+   * @param {number=} opt_timeout How long to wait for the condition to be true.
+   * @param {string=} opt_message An optional message to use if the wait times
+   *     out.
+   * @return {!(promise.Promise<T>|WebElementPromise)} A promise that will be
+   *     resolved with the first truthy value returned by the condition
+   *     function, or rejected if the condition times out. If the input
+   *     input condition is an instance of a {@link WebElementCondition},
+   *     the returned value will be a {@link WebElementPromise}.
+   * @template T
+   */
+  wait(condition, opt_timeout, opt_message) {
+    if (promise.isPromise(condition)) {
+      return this.flow_.wait(
+          /** @type {!promise.Promise} */(condition),
+          opt_timeout, opt_message);
+    }
+
+    var message = opt_message;
+    var fn = /** @type {!Function} */(condition);
+    if (condition instanceof Condition) {
+      message = message || condition.description();
+      fn = condition.fn;
+    }
+
+    var driver = this;
+    var result = this.flow_.wait(function() {
+      if (promise.isGenerator(fn)) {
+        return promise.consume(fn, null, [driver]);
+      }
+      return fn(driver);
+    }, opt_timeout, message);
+
+    if (condition instanceof WebElementCondition) {
+      result = new WebElementPromise(this, result.then(function(value) {
+        if (!(value instanceof WebElement)) {
+          throw TypeError(
+              'WebElementCondition did not resolve to a WebElement: '
+                  + Object.prototype.toString.call(value));
+        }
+        return value;
+      }));
+    }
+    return result;
+  }
+
+  /**
+   * Schedules a command to make the driver sleep for the given amount of time.
+   * @param {number} ms The amount of time, in milliseconds, to sleep.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the sleep has finished.
+   */
+  sleep(ms) {
+    return this.flow_.timeout(ms, 'WebDriver.sleep(' + ms + ')');
+  }
+
+  /**
+   * Schedules a command to retrieve the current window handle.
+   * @return {!promise.Promise<string>} A promise that will be
+   *     resolved with the current window handle.
+   */
+  getWindowHandle() {
+    return this.schedule(
+        new command.Command(command.Name.GET_CURRENT_WINDOW_HANDLE),
+        'WebDriver.getWindowHandle()');
+  }
+
+  /**
+   * Schedules a command to retrieve the current list of available window handles.
+   * @return {!promise.Promise.<!Array<string>>} A promise that will
+   *     be resolved with an array of window handles.
+   */
+  getAllWindowHandles() {
+    return this.schedule(
+        new command.Command(command.Name.GET_WINDOW_HANDLES),
+        'WebDriver.getAllWindowHandles()');
+  }
+
+  /**
+   * Schedules a command to retrieve the current page's source. The page source
+   * returned is a representation of the underlying DOM: do not expect it to be
+   * formatted or escaped in the same way as the response sent from the web
+   * server.
+   * @return {!promise.Promise<string>} A promise that will be
+   *     resolved with the current page source.
+   */
+  getPageSource() {
+    return this.schedule(
+        new command.Command(command.Name.GET_PAGE_SOURCE),
+        'WebDriver.getPageSource()');
+  }
+
+  /**
+   * Schedules a command to close the current window.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when this command has completed.
+   */
+  close() {
+    return this.schedule(new command.Command(command.Name.CLOSE),
+                         'WebDriver.close()');
+  }
+
+  /**
+   * Schedules a command to navigate to the given URL.
+   * @param {string} url The fully qualified URL to open.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the document has finished loading.
+   */
+  get(url) {
+    return this.navigate().to(url);
+  }
+
+  /**
+   * Schedules a command to retrieve the URL of the current page.
+   * @return {!promise.Promise<string>} A promise that will be
+   *     resolved with the current URL.
+   */
+  getCurrentUrl() {
+    return this.schedule(
+        new command.Command(command.Name.GET_CURRENT_URL),
+        'WebDriver.getCurrentUrl()');
+  }
+
+  /**
+   * Schedules a command to retrieve the current page's title.
+   * @return {!promise.Promise<string>} A promise that will be
+   *     resolved with the current page's title.
+   */
+  getTitle() {
+    return this.schedule(new command.Command(command.Name.GET_TITLE),
+                         'WebDriver.getTitle()');
+  }
+
+  /**
+   * Schedule a command to find an element on the page. If the element cannot be
+   * found, a {@link bot.ErrorCode.NO_SUCH_ELEMENT} result will be returned
+   * by the driver. Unlike other commands, this error cannot be suppressed. In
+   * other words, scheduling a command to find an element doubles as an assert
+   * that the element is present on the page. To test whether an element is
+   * present on the page, use {@link #isElementPresent} instead.
+   *
+   * The search criteria for an element may be defined using one of the
+   * factories in the {@link webdriver.By} namespace, or as a short-hand
+   * {@link webdriver.By.Hash} object. For example, the following two statements
+   * are equivalent:
+   *
+   *     var e1 = driver.findElement(By.id('foo'));
+   *     var e2 = driver.findElement({id:'foo'});
+   *
+   * You may also provide a custom locator function, which takes as input this
+   * instance and returns a {@link WebElement}, or a promise that will resolve
+   * to a WebElement. If the returned promise resolves to an array of
+   * WebElements, WebDriver will use the first element. For example, to find the
+   * first visible link on a page, you could write:
+   *
+   *     var link = driver.findElement(firstVisibleLink);
+   *
+   *     function firstVisibleLink(driver) {
+   *       var links = driver.findElements(By.tagName('a'));
+   *       return promise.filter(links, function(link) {
+   *         return link.isDisplayed();
+   *       });
+   *     }
+   *
+   * @param {!(by.By|Function)} locator The locator to use.
+   * @return {!WebElementPromise} A WebElement that can be used to issue
+   *     commands against the located element. If the element is not found, the
+   *     element will be invalidated and all scheduled commands aborted.
+   */
+  findElement(locator) {
+    let id;
+    locator = by.checkedLocator(locator);
+    if (typeof locator === 'function') {
+      id = this.findElementInternal_(locator, this);
+    } else {
+      let cmd = new command.Command(command.Name.FIND_ELEMENT).
+          setParameter('using', locator.using).
+          setParameter('value', locator.value);
+      id = this.schedule(cmd, 'WebDriver.findElement(' + locator + ')');
+    }
+    return new WebElementPromise(this, id);
+  }
+
+  /**
+   * @param {!Function} locatorFn The locator function to use.
+   * @param {!(WebDriver|WebElement)} context The search
+   *     context.
+   * @return {!promise.Promise.<!WebElement>} A
+   *     promise that will resolve to a list of WebElements.
+   * @private
+   */
+  findElementInternal_(locatorFn, context) {
+    return this.call(() => locatorFn(context)).then(function(result) {
+      if (Array.isArray(result)) {
+        result = result[0];
+      }
+      if (!(result instanceof WebElement)) {
+        throw new TypeError('Custom locator did not return a WebElement');
+      }
+      return result;
+    });
+  }
+
+  /**
+   * Schedule a command to search for multiple elements on the page.
+   *
+   * @param {!(by.By|Function)} locator The locator to use.
+   * @return {!promise.Promise.<!Array.<!WebElement>>} A
+   *     promise that will resolve to an array of WebElements.
+   */
+  findElements(locator) {
+    locator = by.checkedLocator(locator);
+    if (typeof locator === 'function') {
+      return this.findElementsInternal_(locator, this);
+    } else {
+      let cmd = new command.Command(command.Name.FIND_ELEMENTS).
+          setParameter('using', locator.using).
+          setParameter('value', locator.value);
+      let res = this.schedule(cmd, 'WebDriver.findElements(' + locator + ')');
+      return res.catch(function(e) {
+        if (e instanceof error.NoSuchElementError) {
+          return [];
+        }
+        throw e;
+      });
+    }
+  }
+
+  /**
+   * @param {!Function} locatorFn The locator function to use.
+   * @param {!(WebDriver|WebElement)} context The search context.
+   * @return {!promise.Promise<!Array<!WebElement>>} A promise that
+   *     will resolve to an array of WebElements.
+   * @private
+   */
+  findElementsInternal_(locatorFn, context) {
+    return this.call(() => locatorFn(context)).then(function(result) {
+      if (result instanceof WebElement) {
+        return [result];
+      }
+
+      if (!Array.isArray(result)) {
+        return [];
+      }
+
+      return result.filter(function(item) {
+        return item instanceof WebElement;
+      });
+    });
+  }
+
+  /**
+   * Schedule a command to take a screenshot. The driver makes a best effort to
+   * return a screenshot of the following, in order of preference:
+   *
+   * 1. Entire page
+   * 2. Current window
+   * 3. Visible portion of the current frame
+   * 4. The entire display containing the browser
+   *
+   * @return {!promise.Promise<string>} A promise that will be
+   *     resolved to the screenshot as a base-64 encoded PNG.
+   */
+  takeScreenshot() {
+    return this.schedule(new command.Command(command.Name.SCREENSHOT),
+        'WebDriver.takeScreenshot()');
+  }
+
+  /**
+   * @return {!Options} The options interface for this instance.
+   */
+  manage() {
+    return new Options(this);
+  }
+
+  /**
+   * @return {!Navigation} The navigation interface for this instance.
+   */
+  navigate() {
+    return new Navigation(this);
+  }
+
+  /**
+   * @return {!TargetLocator} The target locator interface for this
+   *     instance.
+   */
+  switchTo() {
+    return new TargetLocator(this);
+  }
+}
+
+
+/**
+ * Interface for navigating back and forth in the browser history.
+ *
+ * This class should never be instantiated directly. Insead, obtain an instance
+ * with
+ *
+ *    webdriver.navigate()
+ *
+ * @see WebDriver#navigate()
+ */
+class Navigation {
+  /**
+   * @param {!WebDriver} driver The parent driver.
+   * @private
+   */
+  constructor(driver) {
+    /** @private {!WebDriver} */
+    this.driver_ = driver;
+  }
+
+  /**
+   * Schedules a command to navigate to a new URL.
+   * @param {string} url The URL to navigate to.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the URL has been loaded.
+   */
+  to(url) {
+    return this.driver_.schedule(
+        new command.Command(command.Name.GET).
+            setParameter('url', url),
+        'WebDriver.navigate().to(' + url + ')');
+  }
+
+  /**
+   * Schedules a command to move backwards in the browser history.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the navigation event has completed.
+   */
+  back() {
+    return this.driver_.schedule(
+        new command.Command(command.Name.GO_BACK),
+        'WebDriver.navigate().back()');
+  }
+
+  /**
+   * Schedules a command to move forwards in the browser history.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the navigation event has completed.
+   */
+  forward() {
+    return this.driver_.schedule(
+        new command.Command(command.Name.GO_FORWARD),
+        'WebDriver.navigate().forward()');
+  }
+
+  /**
+   * Schedules a command to refresh the current page.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the navigation event has completed.
+   */
+  refresh() {
+    return this.driver_.schedule(
+        new command.Command(command.Name.REFRESH),
+        'WebDriver.navigate().refresh()');
+  }
+}
+
+
+/**
+ * Provides methods for managing browser and driver state.
+ *
+ * This class should never be instantiated directly. Insead, obtain an instance
+ * with {@linkplain WebDriver#manage() webdriver.manage()}.
+ */
+class Options {
+  /**
+   * @param {!WebDriver} driver The parent driver.
+   * @private
+   */
+  constructor(driver) {
+    /** @private {!WebDriver} */
+    this.driver_ = driver;
+  }
+
+  /**
+   * Schedules a command to add a cookie.
+   *
+   * __Sample Usage:__
+   *
+   *     // Set a basic cookie.
+   *     driver.options().addCookie({name: 'foo', value: 'bar'});
+   *
+   *     // Set a cookie that expires in 10 minutes.
+   *     let expiry = new Date(Date.now() + (10 * 60 * 1000));
+   *     driver.options().addCookie({name: 'foo', value: 'bar', expiry});
+   *
+   *     // The cookie expiration may also be specified in seconds since epoch.
+   *     driver.options().addCookie({
+   *       name: 'foo',
+   *       value: 'bar',
+   *       expiry: Math.floor(Date.now() / 1000)
+   *     });
+   *
+   * @param {!Options.Cookie} spec Defines the cookie to add.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the cookie has been added to the page.
+   * @throws {error.InvalidArgumentError} if any of the cookie parameters are
+   *     invalid.
+   * @throws {TypeError} if `spec` is not a cookie object.
+   */
+  addCookie(spec) {
+    if (!spec || typeof spec !== 'object') {
+      throw TypeError('addCookie called with non-cookie parameter');
+    }
+
+    // We do not allow '=' or ';' in the name.
+    let name = spec.name;
+    if (/[;=]/.test(name)) {
+      throw new error.InvalidArgumentError(
+          'Invalid cookie name "' + name + '"');
+    }
+
+    // We do not allow ';' in value.
+    let value = spec.value;
+    if (/;/.test(value)) {
+      throw new error.InvalidArgumentError(
+          'Invalid cookie value "' + value + '"');
+    }
+
+    let cookieString = name + '=' + value +
+        (spec.domain ? ';domain=' + spec.domain : '') +
+        (spec.path ? ';path=' + spec.path : '') +
+        (spec.secure ? ';secure' : '');
+
+    let expiry;
+    if (typeof spec.expiry === 'number') {
+      expiry = Math.floor(spec.expiry);
+      cookieString += ';expires=' + new Date(spec.expiry * 1000).toUTCString();
+    } else if (spec.expiry instanceof Date) {
+      let date = /** @type {!Date} */(spec.expiry);
+      expiry = Math.floor(date.getTime() / 1000);
+      cookieString += ';expires=' + date.toUTCString();
+    }
+
+    return this.driver_.schedule(
+        new command.Command(command.Name.ADD_COOKIE).
+            setParameter('cookie', {
+              'name': name,
+              'value': value,
+              'path': spec.path,
+              'domain': spec.domain,
+              'secure': !!spec.secure,
+              'expiry': expiry
+            }),
+        'WebDriver.manage().addCookie(' + cookieString + ')');
+  }
+
+  /**
+   * Schedules a command to delete all cookies visible to the current page.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when all cookies have been deleted.
+   */
+  deleteAllCookies() {
+    return this.driver_.schedule(
+        new command.Command(command.Name.DELETE_ALL_COOKIES),
+        'WebDriver.manage().deleteAllCookies()');
+  }
+
+  /**
+   * Schedules a command to delete the cookie with the given name. This command
+   * is a no-op if there is no cookie with the given name visible to the current
+   * page.
+   * @param {string} name The name of the cookie to delete.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the cookie has been deleted.
+   */
+  deleteCookie(name) {
+    return this.driver_.schedule(
+        new command.Command(command.Name.DELETE_COOKIE).
+            setParameter('name', name),
+        'WebDriver.manage().deleteCookie(' + name + ')');
+  }
+
+  /**
+   * Schedules a command to retrieve all cookies visible to the current page.
+   * Each cookie will be returned as a JSON object as described by the WebDriver
+   * wire protocol.
+   * @return {!promise.Promise<!Array<!Options.Cookie>>} A promise that will be
+   *     resolved with the cookies visible to the current browsing context.
+   */
+  getCookies() {
+    return this.driver_.schedule(
+        new command.Command(command.Name.GET_ALL_COOKIES),
+        'WebDriver.manage().getCookies()');
+  }
+
+  /**
+   * Schedules a command to retrieve the cookie with the given name. Returns null
+   * if there is no such cookie. The cookie will be returned as a JSON object as
+   * described by the WebDriver wire protocol.
+   *
+   * @param {string} name The name of the cookie to retrieve.
+   * @return {!promise.Promise<?Options.Cookie>} A promise that will be resolved
+   *     with the named cookie, or `null` if there is no such cookie.
+   */
+  getCookie(name) {
+    return this.getCookies().then(function(cookies) {
+      for (let cookie of cookies) {
+        if (cookie && cookie['name'] === name) {
+          return cookie;
+        }
+      }
+      return null;
+    });
+  }
+
+  /**
+   * @return {!Logs} The interface for managing driver
+   *     logs.
+   */
+  logs() {
+    return new Logs(this.driver_);
+  }
+
+  /**
+   * @return {!Timeouts} The interface for managing driver timeouts.
+   */
+  timeouts() {
+    return new Timeouts(this.driver_);
+  }
+
+  /**
+   * @return {!Window} The interface for managing the current window.
+   */
+  window() {
+    return new Window(this.driver_);
+  }
+}
+
+
+/**
+ * A record object describing a browser cookie.
+ *
+ * @record
+ */
+Options.Cookie = function() {};
+
+
+/**
+ * The name of the cookie.
+ *
+ * @type {string}
+ */
+Options.Cookie.prototype.name;
+
+
+/**
+ * The cookie value.
+ *
+ * @type {string}
+ */
+Options.Cookie.prototype.value;
+
+
+/**
+ * The cookie path. Defaults to "/" when adding a cookie.
+ *
+ * @type {(string|undefined)}
+ */
+Options.Cookie.prototype.path;
+
+
+/**
+ * The domain the cookie is visible to. Defaults to the current browsing
+ * context's document's URL when adding a cookie.
+ *
+ * @type {(string|undefined)}
+ */
+Options.Cookie.prototype.domain;
+
+
+/**
+ * Whether the cookie is a secure cookie. Defaults to false when adding a new
+ * cookie.
+ *
+ * @type {(boolean|undefined)}
+ */
+Options.Cookie.prototype.secure;
+
+
+/**
+ * Whether the cookie is an HTTP only cookie. Defaults to false when adding a
+ * new cookie.
+ *
+ * @type {(boolean|undefined)}
+ */
+Options.Cookie.prototype.httpOnly;
+
+
+/**
+ * When the cookie expires.
+ *
+ * When {@linkplain Options#addCookie() adding a cookie}, this may be specified
+ * in _seconds_ since Unix epoch (January 1, 1970). The expiry will default to
+ * 20 years in the future if omitted.
+ *
+ * The expiry is always returned in seconds since epoch when
+ * {@linkplain Options#getCookies() retrieving cookies} from the browser.
+ *
+ * @type {(!Date|number|undefined)}
+ */
+Options.Cookie.prototype.expiry;
+
+
+/**
+ * An interface for managing timeout behavior for WebDriver instances.
+ *
+ * This class should never be instantiated directly. Insead, obtain an instance
+ * with
+ *
+ *    webdriver.manage().timeouts()
+ *
+ * @see WebDriver#manage()
+ * @see Options#timeouts()
+ */
+class Timeouts {
+  /**
+   * @param {!WebDriver} driver The parent driver.
+   * @private
+   */
+  constructor(driver) {
+    /** @private {!WebDriver} */
+    this.driver_ = driver;
+  }
+
+  /**
+   * Specifies the amount of time the driver should wait when searching for an
+   * element if it is not immediately present.
+   *
+   * When searching for a single element, the driver should poll the page
+   * until the element has been found, or this timeout expires before failing
+   * with a {@link bot.ErrorCode.NO_SUCH_ELEMENT} error. When searching
+   * for multiple elements, the driver should poll the page until at least one
+   * element has been found or this timeout has expired.
+   *
+   * Setting the wait timeout to 0 (its default value), disables implicit
+   * waiting.
+   *
+   * Increasing the implicit wait timeout should be used judiciously as it
+   * will have an adverse effect on test run time, especially when used with
+   * slower location strategies like XPath.
+   *
+   * @param {number} ms The amount of time to wait, in milliseconds.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the implicit wait timeout has been set.
+   */
+  implicitlyWait(ms) {
+    return this._scheduleCommand(ms, 'implicit', 'implicitlyWait');
+  }
+
+  /**
+   * Sets the amount of time to wait, in milliseconds, for an asynchronous
+   * script to finish execution before returning an error. If the timeout is
+   * less than or equal to 0, the script will be allowed to run indefinitely.
+   *
+   * @param {number} ms The amount of time to wait, in milliseconds.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the script timeout has been set.
+   */
+  setScriptTimeout(ms) {
+    return this._scheduleCommand(ms, 'script', 'setScriptTimeout');
+  }
+
+  /**
+   * Sets the amount of time to wait for a page load to complete before
+   * returning an error.  If the timeout is negative, page loads may be
+   * indefinite.
+   *
+   * @param {number} ms The amount of time to wait, in milliseconds.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the timeout has been set.
+   */
+  pageLoadTimeout(ms) {
+    return this._scheduleCommand(ms, 'page load', 'pageLoadTimeout');
+  }
+
+  _scheduleCommand(ms, timeoutIdentifier, timeoutName) {
+    return this.driver_.schedule(
+        new command.Command(command.Name.SET_TIMEOUT).
+            setParameter('type', timeoutIdentifier).
+            setParameter('ms', ms),
+        `WebDriver.manage().timeouts().${timeoutName}(${ms})`);
+  }
+}
+
+
+/**
+ * An interface for managing the current window.
+ *
+ * This class should never be instantiated directly. Insead, obtain an instance
+ * with
+ *
+ *    webdriver.manage().window()
+ *
+ * @see WebDriver#manage()
+ * @see Options#window()
+ */
+class Window {
+  /**
+   * @param {!WebDriver} driver The parent driver.
+   * @private
+   */
+  constructor(driver) {
+    /** @private {!WebDriver} */
+    this.driver_ = driver;
+  }
+
+  /**
+   * Retrieves the window's current position, relative to the top left corner of
+   * the screen.
+   * @return {!promise.Promise.<{x: number, y: number}>} A promise
+   *     that will be resolved with the window's position in the form of a
+   *     {x:number, y:number} object literal.
+   */
+  getPosition() {
+    return this.driver_.schedule(
+        new command.Command(command.Name.GET_WINDOW_POSITION).
+            setParameter('windowHandle', 'current'),
+        'WebDriver.manage().window().getPosition()');
+  }
+
+  /**
+   * Repositions the current window.
+   * @param {number} x The desired horizontal position, relative to the left
+   *     side of the screen.
+   * @param {number} y The desired vertical position, relative to the top of the
+   *     of the screen.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the command has completed.
+   */
+  setPosition(x, y) {
+    return this.driver_.schedule(
+        new command.Command(command.Name.SET_WINDOW_POSITION).
+            setParameter('windowHandle', 'current').
+            setParameter('x', x).
+            setParameter('y', y),
+        'WebDriver.manage().window().setPosition(' + x + ', ' + y + ')');
+  }
+
+  /**
+   * Retrieves the window's current size.
+   * @return {!promise.Promise<{width: number, height: number}>} A
+   *     promise that will be resolved with the window's size in the form of a
+   *     {width:number, height:number} object literal.
+   */
+  getSize() {
+    return this.driver_.schedule(
+        new command.Command(command.Name.GET_WINDOW_SIZE).
+            setParameter('windowHandle', 'current'),
+        'WebDriver.manage().window().getSize()');
+  }
+
+  /**
+   * Resizes the current window.
+   * @param {number} width The desired window width.
+   * @param {number} height The desired window height.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the command has completed.
+   */
+  setSize(width, height) {
+    return this.driver_.schedule(
+        new command.Command(command.Name.SET_WINDOW_SIZE).
+            setParameter('windowHandle', 'current').
+            setParameter('width', width).
+            setParameter('height', height),
+        'WebDriver.manage().window().setSize(' + width + ', ' + height + ')');
+  }
+
+  /**
+   * Maximizes the current window.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the command has completed.
+   */
+  maximize() {
+    return this.driver_.schedule(
+        new command.Command(command.Name.MAXIMIZE_WINDOW).
+            setParameter('windowHandle', 'current'),
+        'WebDriver.manage().window().maximize()');
+  }
+}
+
+
+/**
+ * Interface for managing WebDriver log records.
+ *
+ * This class should never be instantiated directly. Instead, obtain an
+ * instance with
+ *
+ *     webdriver.manage().logs()
+ *
+ * @see WebDriver#manage()
+ * @see Options#logs()
+ */
+class Logs {
+  /**
+   * @param {!WebDriver} driver The parent driver.
+   * @private
+   */
+  constructor(driver) {
+    /** @private {!WebDriver} */
+    this.driver_ = driver;
+  }
+
+  /**
+   * Fetches available log entries for the given type.
+   *
+   * Note that log buffers are reset after each call, meaning that available
+   * log entries correspond to those entries not yet returned for a given log
+   * type. In practice, this means that this call will return the available log
+   * entries since the last call, or from the start of the session.
+   *
+   * @param {!logging.Type} type The desired log type.
+   * @return {!promise.Promise.<!Array.<!logging.Entry>>} A
+   *   promise that will resolve to a list of log entries for the specified
+   *   type.
+   */
+  get(type) {
+    let cmd = new command.Command(command.Name.GET_LOG).
+        setParameter('type', type);
+    return this.driver_.schedule(
+        cmd, 'WebDriver.manage().logs().get(' + type + ')').
+        then(function(entries) {
+          return entries.map(function(entry) {
+            if (!(entry instanceof logging.Entry)) {
+              return new logging.Entry(
+                  entry['level'], entry['message'], entry['timestamp'],
+                  entry['type']);
+            }
+            return entry;
+          });
+        });
+  }
+
+  /**
+   * Retrieves the log types available to this driver.
+   * @return {!promise.Promise<!Array<!logging.Type>>} A
+   *     promise that will resolve to a list of available log types.
+   */
+  getAvailableLogTypes() {
+    return this.driver_.schedule(
+        new command.Command(command.Name.GET_AVAILABLE_LOG_TYPES),
+        'WebDriver.manage().logs().getAvailableLogTypes()');
+  }
+}
+
+
+/**
+ * An interface for changing the focus of the driver to another frame or window.
+ *
+ * This class should never be instantiated directly. Instead, obtain an
+ * instance with
+ *
+ *     webdriver.switchTo()
+ *
+ * @see WebDriver#switchTo()
+ */
+class TargetLocator {
+  /**
+   * @param {!WebDriver} driver The parent driver.
+   * @private
+   */
+  constructor(driver) {
+    /** @private {!WebDriver} */
+    this.driver_ = driver;
+  }
+
+  /**
+   * Schedules a command retrieve the {@code document.activeElement} element on
+   * the current document, or {@code document.body} if activeElement is not
+   * available.
+   * @return {!WebElementPromise} The active element.
+   */
+  activeElement() {
+    var id = this.driver_.schedule(
+        new command.Command(command.Name.GET_ACTIVE_ELEMENT),
+        'WebDriver.switchTo().activeElement()');
+    return new WebElementPromise(this.driver_, id);
+  }
+
+  /**
+   * Schedules a command to switch focus of all future commands to the topmost
+   * frame on the page.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the driver has changed focus to the default content.
+   */
+  defaultContent() {
+    return this.driver_.schedule(
+        new command.Command(command.Name.SWITCH_TO_FRAME).
+            setParameter('id', null),
+        'WebDriver.switchTo().defaultContent()');
+  }
+
+  /**
+   * Schedules a command to switch the focus of all future commands to another
+   * frame on the page. The target frame may be specified as one of the
+   * following:
+   *
+   * - A number that specifies a (zero-based) index into [window.frames](
+   *   https://developer.mozilla.org/en-US/docs/Web/API/Window.frames).
+   * - A {@link WebElement} reference, which correspond to a `frame` or `iframe`
+   *   DOM element.
+   * - The `null` value, to select the topmost frame on the page. Passing `null`
+   *   is the same as calling {@link #defaultContent defaultContent()}.
+   *
+   * If the specified frame can not be found, the returned promise will be
+   * rejected with a {@linkplain error.NoSuchFrameError}.
+   *
+   * @param {(number|WebElement|null)} id The frame locator.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the driver has changed focus to the specified frame.
+   */
+  frame(id) {
+    return this.driver_.schedule(
+        new command.Command(command.Name.SWITCH_TO_FRAME).
+            setParameter('id', id),
+        'WebDriver.switchTo().frame(' + id + ')');
+  }
+
+  /**
+   * Schedules a command to switch the focus of all future commands to another
+   * window. Windows may be specified by their {@code window.name} attribute or
+   * by its handle (as returned by {@link WebDriver#getWindowHandles}).
+   *
+   * If the specified window cannot be found, the returned promise will be
+   * rejected with a {@linkplain error.NoSuchWindowError}.
+   *
+   * @param {string} nameOrHandle The name or window handle of the window to
+   *     switch focus to.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the driver has changed focus to the specified window.
+   */
+  window(nameOrHandle) {
+    return this.driver_.schedule(
+        new command.Command(command.Name.SWITCH_TO_WINDOW).
+            // "name" supports the legacy drivers. "handle" is the W3C
+            // compliant parameter.
+            setParameter('name', nameOrHandle).
+            setParameter('handle', nameOrHandle),
+        'WebDriver.switchTo().window(' + nameOrHandle + ')');
+  }
+
+  /**
+   * Schedules a command to change focus to the active modal dialog, such as
+   * those opened by `window.alert()`, `window.confirm()`, and
+   * `window.prompt()`. The returned promise will be rejected with a
+   * {@linkplain error.NoSuchAlertError} if there are no open alerts.
+   *
+   * @return {!AlertPromise} The open alert.
+   */
+  alert() {
+    var text = this.driver_.schedule(
+        new command.Command(command.Name.GET_ALERT_TEXT),
+        'WebDriver.switchTo().alert()');
+    var driver = this.driver_;
+    return new AlertPromise(driver, text.then(function(text) {
+      return new Alert(driver, text);
+    }));
+  }
+}
+
+
+//////////////////////////////////////////////////////////////////////////////
+//
+//  WebElement
+//
+//////////////////////////////////////////////////////////////////////////////
+
+
+const LEGACY_ELEMENT_ID_KEY = 'ELEMENT';
+const ELEMENT_ID_KEY = 'element-6066-11e4-a52e-4f735466cecf';
+
+
+/**
+ * Represents a DOM element. WebElements can be found by searching from the
+ * document root using a {@link WebDriver} instance, or by searching
+ * under another WebElement:
+ *
+ *     driver.get('http://www.google.com');
+ *     var searchForm = driver.findElement(By.tagName('form'));
+ *     var searchBox = searchForm.findElement(By.name('q'));
+ *     searchBox.sendKeys('webdriver');
+ */
+class WebElement {
+  /**
+   * @param {!WebDriver} driver the parent WebDriver instance for this element.
+   * @param {(!IThenable<string>|string)} id The server-assigned opaque ID for
+   *     the underlying DOM element.
+   */
+  constructor(driver, id) {
+    /** @private {!WebDriver} */
+    this.driver_ = driver;
+
+    /** @private {!promise.Promise<string>} */
+    this.id_ = promise.fulfilled(id);
+  }
+
+  /**
+   * @param {string} id The raw ID.
+   * @param {boolean=} opt_noLegacy Whether to exclude the legacy element key.
+   * @return {!Object} The element ID for use with WebDriver's wire protocol.
+   */
+  static buildId(id, opt_noLegacy) {
+    return opt_noLegacy
+        ? {[ELEMENT_ID_KEY]: id}
+        : {[ELEMENT_ID_KEY]: id, [LEGACY_ELEMENT_ID_KEY]: id};
+  }
+
+  /**
+   * Extracts the encoded WebElement ID from the object.
+   *
+   * @param {?} obj The object to extract the ID from.
+   * @return {string} the extracted ID.
+   * @throws {TypeError} if the object is not a valid encoded ID.
+   */
+  static extractId(obj) {
+    if (obj && typeof obj === 'object') {
+      if (typeof obj[ELEMENT_ID_KEY] === 'string') {
+        return obj[ELEMENT_ID_KEY];
+      } else if (typeof obj[LEGACY_ELEMENT_ID_KEY] === 'string') {
+        return obj[LEGACY_ELEMENT_ID_KEY];
+      }
+    }
+    throw new TypeError('object is not a WebElement ID');
+  }
+
+  /**
+   * @param {?} obj the object to test.
+   * @return {boolean} whether the object is a valid encoded WebElement ID.
+   */
+  static isId(obj) {
+    return obj && typeof obj === 'object'
+        && (typeof obj[ELEMENT_ID_KEY] === 'string'
+            || typeof obj[LEGACY_ELEMENT_ID_KEY] === 'string');
+  }
+
+  /**
+   * Compares two WebElements for equality.
+   *
+   * @param {!WebElement} a A WebElement.
+   * @param {!WebElement} b A WebElement.
+   * @return {!promise.Promise<boolean>} A promise that will be
+   *     resolved to whether the two WebElements are equal.
+   */
+  static equals(a, b) {
+    if (a === b) {
+      return promise.fulfilled(true);
+    }
+    let ids = [a.getId(), b.getId()];
+    return promise.all(ids).then(function(ids) {
+      // If the two element's have the same ID, they should be considered
+      // equal. Otherwise, they may still be equivalent, but we'll need to
+      // ask the server to check for us.
+      if (ids[0] === ids[1]) {
+        return true;
+      }
+
+      let cmd = new command.Command(command.Name.ELEMENT_EQUALS);
+      cmd.setParameter('id', ids[0]);
+      cmd.setParameter('other', ids[1]);
+      return a.driver_.schedule(cmd, 'WebElement.equals()');
+    });
+  }
+
+  /** @return {!WebDriver} The parent driver for this instance. */
+  getDriver() {
+    return this.driver_;
+  }
+
+  /**
+   * @return {!promise.Promise<string>} A promise that resolves to
+   *     the server-assigned opaque ID assigned to this element.
+   */
+  getId() {
+    return this.id_;
+  }
+
+  /**
+   * @return {!Object} Returns the serialized representation of this WebElement.
+   */
+  [Symbols.serialize]() {
+    return this.getId().then(WebElement.buildId);
+  }
+
+  /**
+   * Schedules a command that targets this element with the parent WebDriver
+   * instance. Will ensure this element's ID is included in the command
+   * parameters under the "id" key.
+   *
+   * @param {!command.Command} command The command to schedule.
+   * @param {string} description A description of the command for debugging.
+   * @return {!promise.Promise<T>} A promise that will be resolved
+   *     with the command result.
+   * @template T
+   * @see WebDriver#schedule
+   * @private
+   */
+  schedule_(command, description) {
+    command.setParameter('id', this.getId());
+    return this.driver_.schedule(command, description);
+  }
+
+  /**
+   * Schedule a command to find a descendant of this element. If the element
+   * cannot be found, the returned promise will be rejected with a
+   * {@linkplain error.NoSuchElementError NoSuchElementError}.
+   *
+   * The search criteria for an element may be defined using one of the static
+   * factories on the {@link by.By} class, or as a short-hand
+   * {@link ./by.ByHash} object. For example, the following two statements
+   * are equivalent:
+   *
+   *     var e1 = element.findElement(By.id('foo'));
+   *     var e2 = element.findElement({id:'foo'});
+   *
+   * You may also provide a custom locator function, which takes as input this
+   * instance and returns a {@link WebElement}, or a promise that will resolve
+   * to a WebElement. If the returned promise resolves to an array of
+   * WebElements, WebDriver will use the first element. For example, to find the
+   * first visible link on a page, you could write:
+   *
+   *     var link = element.findElement(firstVisibleLink);
+   *
+   *     function firstVisibleLink(element) {
+   *       var links = element.findElements(By.tagName('a'));
+   *       return promise.filter(links, function(link) {
+   *         return link.isDisplayed();
+   *       });
+   *     }
+   *
+   * @param {!(by.By|Function)} locator The locator strategy to use when
+   *     searching for the element.
+   * @return {!WebElementPromise} A WebElement that can be used to issue
+   *     commands against the located element. If the element is not found, the
+   *     element will be invalidated and all scheduled commands aborted.
+   */
+  findElement(locator) {
+    locator = by.checkedLocator(locator);
+    let id;
+    if (typeof locator === 'function') {
+      id = this.driver_.findElementInternal_(locator, this);
+    } else {
+      let cmd = new command.Command(
+          command.Name.FIND_CHILD_ELEMENT).
+          setParameter('using', locator.using).
+          setParameter('value', locator.value);
+      id = this.schedule_(cmd, 'WebElement.findElement(' + locator + ')');
+    }
+    return new WebElementPromise(this.driver_, id);
+  }
+
+  /**
+   * Schedules a command to find all of the descendants of this element that
+   * match the given search criteria.
+   *
+   * @param {!(by.By|Function)} locator The locator strategy to use when
+   *     searching for the element.
+   * @return {!promise.Promise<!Array<!WebElement>>} A
+   *     promise that will resolve to an array of WebElements.
+   */
+  findElements(locator) {
+    locator = by.checkedLocator(locator);
+    let id;
+    if (typeof locator === 'function') {
+      return this.driver_.findElementsInternal_(locator, this);
+    } else {
+      var cmd = new command.Command(
+          command.Name.FIND_CHILD_ELEMENTS).
+          setParameter('using', locator.using).
+          setParameter('value', locator.value);
+      return this.schedule_(cmd, 'WebElement.findElements(' + locator + ')');
+    }
+  }
+
+  /**
+   * Schedules a command to click on this element.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the click command has completed.
+   */
+  click() {
+    return this.schedule_(
+        new command.Command(command.Name.CLICK_ELEMENT),
+        'WebElement.click()');
+  }
+
+  /**
+   * Schedules a command to type a sequence on the DOM element represented by
+   * this instance.
+   *
+   * Modifier keys (SHIFT, CONTROL, ALT, META) are stateful; once a modifier is
+   * processed in the keysequence, that key state is toggled until one of the
+   * following occurs:
+   *
+   * - The modifier key is encountered again in the sequence. At this point the
+   *   state of the key is toggled (along with the appropriate keyup/down
+   *   events).
+   * - The {@link input.Key.NULL} key is encountered in the sequence. When
+   *   this key is encountered, all modifier keys current in the down state are
+   *   released (with accompanying keyup events). The NULL key can be used to
+   *   simulate common keyboard shortcuts:
+   *
+   *         element.sendKeys("text was",
+   *                          Key.CONTROL, "a", Key.NULL,
+   *                          "now text is");
+   *         // Alternatively:
+   *         element.sendKeys("text was",
+   *                          Key.chord(Key.CONTROL, "a"),
+   *                          "now text is");
+   *
+   * - The end of the keysequence is encountered. When there are no more keys
+   *   to type, all depressed modifier keys are released (with accompanying
+   *   keyup events).
+   *
+   * If this element is a file input ({@code <input type="file">}), the
+   * specified key sequence should specify the path to the file to attach to
+   * the element. This is analgous to the user clicking "Browse..." and entering
+   * the path into the file select dialog.
+   *
+   *     var form = driver.findElement(By.css('form'));
+   *     var element = form.findElement(By.css('input[type=file]'));
+   *     element.sendKeys('/path/to/file.txt');
+   *     form.submit();
+   *
+   * For uploads to function correctly, the entered path must reference a file
+   * on the _browser's_ machine, not the local machine running this script. When
+   * running against a remote Selenium server, a {@link input.FileDetector}
+   * may be used to transparently copy files to the remote machine before
+   * attempting to upload them in the browser.
+   *
+   * __Note:__ On browsers where native keyboard events are not supported
+   * (e.g. Firefox on OS X), key events will be synthesized. Special
+   * punctionation keys will be synthesized according to a standard QWERTY en-us
+   * keyboard layout.
+   *
+   * @param {...(number|string|!IThenable<(number|string)>)} var_args The
+   *     sequence of keys to type. Number keys may be referenced numerically or
+   *     by string (1 or '1'). All arguments will be joined into a single
+   *     sequence.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when all keys have been typed.
+   */
+  sendKeys(var_args) {
+    let keys = Promise.all(Array.prototype.slice.call(arguments, 0)).
+        then(keys => {
+          let ret = [];
+          keys.forEach(key => {
+            let type = typeof key;
+            if (type === 'number') {
+              key = String(key);
+            } else if (type !== 'string') {
+              throw TypeError(
+                  'each key must be a number of string; got ' + type);
+            }
+
+            // The W3C protocol requires keys to be specified as an array where
+            // each element is a single key.
+            ret.push.apply(ret, key.split(''));
+          });
+          return ret;
+        });
+
+    if (!this.driver_.fileDetector_) {
+      return this.schedule_(
+          new command.Command(command.Name.SEND_KEYS_TO_ELEMENT).
+              setParameter('value', keys),
+          'WebElement.sendKeys()');
+    }
+
+    // Suppress unhandled rejection errors until the flow executes the command.
+    keys.catch(function() {});
+
+    var element = this;
+    return this.driver_.flow_.execute(function() {
+      return keys.then(function(keys) {
+        return element.driver_.fileDetector_
+            .handleFile(element.driver_, keys.join(''));
+      }).then(function(keys) {
+        return element.schedule_(
+            new command.Command(command.Name.SEND_KEYS_TO_ELEMENT).
+                setParameter('value', keys.split('')),
+            'WebElement.sendKeys()');
+      });
+    }, 'WebElement.sendKeys()');
+  }
+
+  /**
+   * Schedules a command to query for the tag/node name of this element.
+   * @return {!promise.Promise<string>} A promise that will be
+   *     resolved with the element's tag name.
+   */
+  getTagName() {
+    return this.schedule_(
+        new command.Command(command.Name.GET_ELEMENT_TAG_NAME),
+        'WebElement.getTagName()');
+  }
+
+  /**
+   * Schedules a command to query for the computed style of the element
+   * represented by this instance. If the element inherits the named style from
+   * its parent, the parent will be queried for its value.  Where possible, color
+   * values will be converted to their hex representation (e.g. #00ff00 instead
+   * of rgb(0, 255, 0)).
+   *
+   * _Warning:_ the value returned will be as the browser interprets it, so
+   * it may be tricky to form a proper assertion.
+   *
+   * @param {string} cssStyleProperty The name of the CSS style property to look
+   *     up.
+   * @return {!promise.Promise<string>} A promise that will be
+   *     resolved with the requested CSS value.
+   */
+  getCssValue(cssStyleProperty) {
+    var name = command.Name.GET_ELEMENT_VALUE_OF_CSS_PROPERTY;
+    return this.schedule_(
+        new command.Command(name).
+            setParameter('propertyName', cssStyleProperty),
+        'WebElement.getCssValue(' + cssStyleProperty + ')');
+  }
+
+  /**
+   * Schedules a command to query for the value of the given attribute of the
+   * element. Will return the current value, even if it has been modified after
+   * the page has been loaded. More exactly, this method will return the value
+   * of the given attribute, unless that attribute is not present, in which case
+   * the value of the property with the same name is returned. If neither value
+   * is set, null is returned (for example, the "value" property of a textarea
+   * element). The "style" attribute is converted as best can be to a
+   * text representation with a trailing semi-colon. The following are deemed to
+   * be "boolean" attributes and will return either "true" or null:
+   *
+   * async, autofocus, autoplay, checked, compact, complete, controls, declare,
+   * defaultchecked, defaultselected, defer, disabled, draggable, ended,
+   * formnovalidate, hidden, indeterminate, iscontenteditable, ismap, itemscope,
+   * loop, multiple, muted, nohref, noresize, noshade, novalidate, nowrap, open,
+   * paused, pubdate, readonly, required, reversed, scoped, seamless, seeking,
+   * selected, spellcheck, truespeed, willvalidate
+   *
+   * Finally, the following commonly mis-capitalized attribute/property names
+   * are evaluated as expected:
+   *
+   * - "class"
+   * - "readonly"
+   *
+   * @param {string} attributeName The name of the attribute to query.
+   * @return {!promise.Promise<?string>} A promise that will be
+   *     resolved with the attribute's value. The returned value will always be
+   *     either a string or null.
+   */
+  getAttribute(attributeName) {
+    return this.schedule_(
+        new command.Command(command.Name.GET_ELEMENT_ATTRIBUTE).
+            setParameter('name', attributeName),
+        'WebElement.getAttribute(' + attributeName + ')');
+  }
+
+  /**
+   * Get the visible (i.e. not hidden by CSS) innerText of this element,
+   * including sub-elements, without any leading or trailing whitespace.
+   *
+   * @return {!promise.Promise<string>} A promise that will be
+   *     resolved with the element's visible text.
+   */
+  getText() {
+    return this.schedule_(
+        new command.Command(command.Name.GET_ELEMENT_TEXT),
+        'WebElement.getText()');
+  }
+
+  /**
+   * Schedules a command to compute the size of this element's bounding box, in
+   * pixels.
+   * @return {!promise.Promise.<{width: number, height: number}>} A
+   *     promise that will be resolved with the element's size as a
+   *     {@code {width:number, height:number}} object.
+   */
+  getSize() {
+    return this.schedule_(
+        new command.Command(command.Name.GET_ELEMENT_SIZE),
+        'WebElement.getSize()');
+  }
+
+  /**
+   * Schedules a command to compute the location of this element in page space.
+   * @return {!promise.Promise.<{x: number, y: number}>} A promise that
+   *     will be resolved to the element's location as a
+   *     {@code {x:number, y:number}} object.
+   */
+  getLocation() {
+    return this.schedule_(
+        new command.Command(command.Name.GET_ELEMENT_LOCATION),
+        'WebElement.getLocation()');
+  }
+
+  /**
+   * Schedules a command to query whether the DOM element represented by this
+   * instance is enabled, as dicted by the {@code disabled} attribute.
+   * @return {!promise.Promise<boolean>} A promise that will be
+   *     resolved with whether this element is currently enabled.
+   */
+  isEnabled() {
+    return this.schedule_(
+        new command.Command(command.Name.IS_ELEMENT_ENABLED),
+        'WebElement.isEnabled()');
+  }
+
+  /**
+   * Schedules a command to query whether this element is selected.
+   * @return {!promise.Promise<boolean>} A promise that will be
+   *     resolved with whether this element is currently selected.
+   */
+  isSelected() {
+    return this.schedule_(
+        new command.Command(command.Name.IS_ELEMENT_SELECTED),
+        'WebElement.isSelected()');
+  }
+
+  /**
+   * Schedules a command to submit the form containing this element (or this
+   * element if it is a FORM element). This command is a no-op if the element is
+   * not contained in a form.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the form has been submitted.
+   */
+  submit() {
+    return this.schedule_(
+        new command.Command(command.Name.SUBMIT_ELEMENT),
+        'WebElement.submit()');
+  }
+
+  /**
+   * Schedules a command to clear the `value` of this element. This command has
+   * no effect if the underlying DOM element is neither a text INPUT element
+   * nor a TEXTAREA element.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when the element has been cleared.
+   */
+  clear() {
+    return this.schedule_(
+        new command.Command(command.Name.CLEAR_ELEMENT),
+        'WebElement.clear()');
+  }
+
+  /**
+   * Schedules a command to test whether this element is currently displayed.
+   * @return {!promise.Promise<boolean>} A promise that will be
+   *     resolved with whether this element is currently visible on the page.
+   */
+  isDisplayed() {
+    return this.schedule_(
+        new command.Command(command.Name.IS_ELEMENT_DISPLAYED),
+        'WebElement.isDisplayed()');
+  }
+
+  /**
+   * Take a screenshot of the visible region encompassed by this element's
+   * bounding rectangle.
+   *
+   * @param {boolean=} opt_scroll Optional argument that indicates whether the
+   *     element should be scrolled into view before taking a screenshot.
+   *     Defaults to false.
+   * @return {!promise.Promise<string>} A promise that will be
+   *     resolved to the screenshot as a base-64 encoded PNG.
+   */
+  takeScreenshot(opt_scroll) {
+    var scroll = !!opt_scroll;
+    return this.schedule_(
+        new command.Command(command.Name.TAKE_ELEMENT_SCREENSHOT)
+            .setParameter('scroll', scroll),
+        'WebElement.takeScreenshot(' + scroll + ')');
+  }
+}
+
+
+/**
+ * WebElementPromise is a promise that will be fulfilled with a WebElement.
+ * This serves as a forward proxy on WebElement, allowing calls to be
+ * scheduled without directly on this instance before the underlying
+ * WebElement has been fulfilled. In other words, the following two statements
+ * are equivalent:
+ *
+ *     driver.findElement({id: 'my-button'}).click();
+ *     driver.findElement({id: 'my-button'}).then(function(el) {
+ *       return el.click();
+ *     });
+ *
+ * @implements {promise.Thenable<!WebElement>}
+ * @final
+ */
+class WebElementPromise extends WebElement {
+  /**
+   * @param {!WebDriver} driver The parent WebDriver instance for this
+   *     element.
+   * @param {!promise.Promise<!WebElement>} el A promise
+   *     that will resolve to the promised element.
+   */
+  constructor(driver, el) {
+    super(driver, 'unused');
+
+    /** @override */
+    this.cancel = el.cancel.bind(el);
+
+    /** @override */
+    this.isPending = el.isPending.bind(el);
+
+    /** @override */
+    this.then = el.then.bind(el);
+
+    /** @override */
+    this.catch = el.catch.bind(el);
+
+    /** @override */
+    this.finally = el.finally.bind(el);
+
+    /**
+     * Defers returning the element ID until the wrapped WebElement has been
+     * resolved.
+     * @override
+     */
+    this.getId = function() {
+      return el.then(function(el) {
+        return el.getId();
+      });
+    };
+  }
+}
+promise.Thenable.addImplementation(WebElementPromise);
+
+
+//////////////////////////////////////////////////////////////////////////////
+//
+//  Alert
+//
+//////////////////////////////////////////////////////////////////////////////
+
+
+/**
+ * Represents a modal dialog such as {@code alert}, {@code confirm}, or
+ * {@code prompt}. Provides functions to retrieve the message displayed with
+ * the alert, accept or dismiss the alert, and set the response text (in the
+ * case of {@code prompt}).
+ */
+class Alert {
+  /**
+   * @param {!WebDriver} driver The driver controlling the browser this alert
+   *     is attached to.
+   * @param {string} text The message text displayed with this alert.
+   */
+  constructor(driver, text) {
+    /** @private {!WebDriver} */
+    this.driver_ = driver;
+
+    /** @private {!promise.Promise<string>} */
+    this.text_ = promise.fulfilled(text);
+  }
+
+  /**
+   * Retrieves the message text displayed with this alert. For instance, if the
+   * alert were opened with alert("hello"), then this would return "hello".
+   *
+   * @return {!promise.Promise<string>} A promise that will be
+   *     resolved to the text displayed with this alert.
+   */
+  getText() {
+    return this.text_;
+  }
+
+  /**
+   * Sets the username and password in an alert prompting for credentials (such
+   * as a Basic HTTP Auth prompt). This method will implicitly
+   * {@linkplain #accept() submit} the dialog.
+   *
+   * @param {string} username The username to send.
+   * @param {string} password The password to send.
+   * @return {!promise.Promise<void>} A promise that will be resolved when this
+   *     command has completed.
+   */
+  authenticateAs(username, password) {
+    return this.driver_.schedule(
+        new command.Command(command.Name.SET_ALERT_CREDENTIALS),
+        'WebDriver.switchTo().alert()'
+            + `.authenticateAs("${username}", "${password}")`);
+  }
+
+  /**
+   * Accepts this alert.
+   *
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when this command has completed.
+   */
+  accept() {
+    return this.driver_.schedule(
+        new command.Command(command.Name.ACCEPT_ALERT),
+        'WebDriver.switchTo().alert().accept()');
+  }
+
+  /**
+   * Dismisses this alert.
+   *
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when this command has completed.
+   */
+  dismiss() {
+    return this.driver_.schedule(
+        new command.Command(command.Name.DISMISS_ALERT),
+        'WebDriver.switchTo().alert().dismiss()');
+  }
+
+  /**
+   * Sets the response text on this alert. This command will return an error if
+   * the underlying alert does not support response text (e.g. window.alert and
+   * window.confirm).
+   *
+   * @param {string} text The text to set.
+   * @return {!promise.Promise<void>} A promise that will be resolved
+   *     when this command has completed.
+   */
+  sendKeys(text) {
+    return this.driver_.schedule(
+        new command.Command(command.Name.SET_ALERT_TEXT).
+            setParameter('text', text),
+        'WebDriver.switchTo().alert().sendKeys(' + text + ')');
+  }
+}
+
+
+/**
+ * AlertPromise is a promise that will be fulfilled with an Alert. This promise
+ * serves as a forward proxy on an Alert, allowing calls to be scheduled
+ * directly on this instance before the underlying Alert has been fulfilled. In
+ * other words, the following two statements are equivalent:
+ *
+ *     driver.switchTo().alert().dismiss();
+ *     driver.switchTo().alert().then(function(alert) {
+ *       return alert.dismiss();
+ *     });
+ *
+ * @implements {promise.Thenable.<!webdriver.Alert>}
+ * @final
+ */
+class AlertPromise extends Alert {
+  /**
+   * @param {!WebDriver} driver The driver controlling the browser this
+   *     alert is attached to.
+   * @param {!promise.Thenable<!Alert>} alert A thenable
+   *     that will be fulfilled with the promised alert.
+   */
+  constructor(driver, alert) {
+    super(driver, 'unused');
+
+    /** @override */
+    this.cancel = alert.cancel.bind(alert);
+
+    /** @override */
+    this.isPending = alert.isPending.bind(alert);
+
+    /** @override */
+    this.then = alert.then.bind(alert);
+
+    /** @override */
+    this.catch = alert.catch.bind(alert);
+
+    /** @override */
+    this.finally = alert.finally.bind(alert);
+
+    /**
+     * Defer returning text until the promised alert has been resolved.
+     * @override
+     */
+    this.getText = function() {
+      return alert.then(function(alert) {
+        return alert.getText();
+      });
+    };
+
+    /**
+     * Defers action until the alert has been located.
+     * @override
+     */
+    this.authenticateAs = function(username, password) {
+      return alert.then(function(alert) {
+        return alert.authenticateAs(username, password);
+      });
+    };
+
+    /**
+     * Defers action until the alert has been located.
+     * @override
+     */
+    this.accept = function() {
+      return alert.then(function(alert) {
+        return alert.accept();
+      });
+    };
+
+    /**
+     * Defers action until the alert has been located.
+     * @override
+     */
+    this.dismiss = function() {
+      return alert.then(function(alert) {
+        return alert.dismiss();
+      });
+    };
+
+    /**
+     * Defers action until the alert has been located.
+     * @override
+     */
+    this.sendKeys = function(text) {
+      return alert.then(function(alert) {
+        return alert.sendKeys(text);
+      });
+    };
+  }
+}
+promise.Thenable.addImplementation(AlertPromise);
+
+
+// PUBLIC API
+
+
+module.exports = {
+  Alert: Alert,
+  AlertPromise: AlertPromise,
+  Condition: Condition,
+  Logs: Logs,
+  Navigation: Navigation,
+  Options: Options,
+  TargetLocator: TargetLocator,
+  Timeouts: Timeouts,
+  WebDriver: WebDriver,
+  WebElement: WebElement,
+  WebElementCondition: WebElementCondition,
+  WebElementPromise: WebElementPromise,
+  Window: Window
+};