Port braille related tests from ChromeVox upstream.

chrome/browser/resources/chromeos/chromevox/testing/fake_objects.js

+// Copyright 2014 The Chromium Authors. All rights reserved.

[David Tseng, 2014/09/08 21:45:59]

Maybe call this file fake_event.js?

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * Fakes a Chrome event that supports one listener.
+ * @constructor

[David Tseng, 2014/09/08 21:45:59]

Can you inherit from a ChromeEvent?

[David Tseng, 2014/09/09 20:37:48]

Maybe call this class FakeChromeEvent then :).

+ */
+function FakeEvent() {
+  /** @private {Function} */

[David Tseng, 2014/09/08 21:46:00]

Is this valid js doc?

+  this.listener_ = null;
+}
+
+FakeEvent.prototype = {
+  /**
+   * Fakes the corresponding call on a Chrome event.  Sets the listener and
+   * fails the test if it is already set.

[David Tseng, 2014/09/08 21:45:59]

Why? This isn't the behavior of ChromeEvent.

+   * @param {Function} listener The new listener.
+   */
+  addListener: function(listener) {
+    this.assertNoListener();
+    this.listener_ = listener;
+  },
+
+  /**
+   * Gets the listener of the event, failing the test if there's noone.

[David Tseng, 2014/09/08 21:45:59]

nit: none

+   * @return {Function} The event's listener.
+   */
+  getListener: function() {

[David Tseng, 2014/09/08 21:45:59]

Is this part of the ChromeEvent interface?

+    assertNotEquals(null, this.listener_);
+    return this.listener_;
+  },
+
+  /**
+   * Asserts that this object doesn't have any listener added.
+   */
+  assertNoListener: function() {
+    assertEquals(null, this.listener_);
+  }
+};