[MD Bookmarks] Refactor window timer mocking.

chrome/test/data/webui/md_bookmarks/md_bookmarks_browsertest.js

 // Copyright 2016 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.
 
 /**
  * @fileoverview Test suite for the Material Design bookmarks page.
  */
 var ROOT_PATH = '../../../../../';
 
 GEN_INCLUDE(
@@ skipping 10 matching lines @@
   browsePreload: 'chrome://bookmarks',
 
   commandLineSwitches: [{switchName: 'enable-features',
                          switchValue: 'MaterialDesignBookmarks'}],
 
   typedefCppFixture: 'MdBookmarksBrowserTest',
 
   extraLibraries: PolymerTest.getLibraries(ROOT_PATH).concat([
     'test_command_manager.js',
     'test_store.js',
+    'test_timer_proxy.js',
     'test_util.js',
   ]),
 };
 
 function MaterialBookmarksActionsTest() {}
 
 MaterialBookmarksActionsTest.prototype = {
   __proto__: MaterialBookmarksBrowserTest.prototype,
 
   extraLibraries: MaterialBookmarksBrowserTest.prototype.extraLibraries.concat([
@@ skipping 198 matching lines @@
   __proto__: MaterialBookmarksBrowserTest.prototype,
 
   extraLibraries: MaterialBookmarksBrowserTest.prototype.extraLibraries.concat([
     'util_test.js',
   ]),
 };
 
 TEST_F('MaterialBookmarksUtilTest', 'All', function() {
   mocha.run();
 });