Fix tests flakes.

chrome/browser/resources/chromeos/chromevox/cvox2/background/background_test.extjs

 // 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.
 
 // Include test fixture.
 GEN_INCLUDE(['../../testing/chromevox_next_e2e_test_base.js',
              '../../testing/assert_additions.js']);
 
 GEN_INCLUDE(['../../testing/mock_feedback.js']);
 
 /**
  * Test fixture for Background.
  * @constructor
  * @extends {ChromeVoxNextE2ETest}
  */
 function BackgroundTest() {
   ChromeVoxNextE2ETest.call(this);
 }
 
 BackgroundTest.prototype = {
   __proto__: ChromeVoxNextE2ETest.prototype,
 
   /** @override */
   setUp: function() {
     ChromeVoxState.instance.toggleNext(true);
     window.RoleType = chrome.automation.RoleType;
     window.doCmd = this.doCmd;
+
+    // Reset notifications so only explicit mode changes can cause them to trigger.
+    Notifications.reset();
   },
 
   /**
    * @return {!MockFeedback}
    */
   createMockFeedback: function() {
     var mockFeedback = new MockFeedback(this.newCallback(),
                                         this.newCallback.bind(this));
     mockFeedback.install();
     return mockFeedback;
@@ skipping 919 matching lines @@
         .call(assertRangeHasText('Top News'))
         .call(doCmd('nextHeading'))
         .expectSpeech('Most Popular')
         .call(assertRangeHasText('Most Popular'))
         .call(doCmd('nextLine'))
         .expectSpeech('Sports')
         .call(assertRangeHasText('Sports'))
         .replay();
   });
 });