Port braille related tests from ChromeVox upstream.

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

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// 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
+ * @extends {ChromeEvent}
+ */
+function FakeChromeEvent() {
+  /**
+   * @private
+   * @type {Function}
+   */
+  this.listener_ = null;
+}
+
+FakeChromeEvent.prototype = {
+  /**
+   * Fakes the corresponding call on a Chrome event.  Sets the listener and
+   * fails the test if it is already set.
+   * @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 none.
+   * @return {Function} The event's listener.
+   */
+  getListener: function() {
+    assertNotEquals(null, this.listener_);
+    return this.listener_;
+  },
+
+  /**
+   * Asserts that this object doesn't have any listener added.
+   */
+  assertNoListener: function() {
+    assertEquals(null, this.listener_);
+  }
+};