[MD History] Reenable SyncedTabsTest.

chrome/test/data/webui/md_history/md_history_browsertest.js

 // Copyright 2015 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 history page.
  */
 
 var ROOT_PATH = '../../../../../';
 
@@ skipping 196 matching lines @@
 function MaterialHistorySyncedTabsTest() {}
 
 MaterialHistorySyncedTabsTest.prototype = {
   __proto__: MaterialHistoryBrowserTest.prototype,
 
   extraLibraries: MaterialHistoryBrowserTest.prototype.extraLibraries.concat([
     'history_synced_tabs_test.js',
   ]),
 };
 
-// Fails on Mac, http://crbug.com/640862
-TEST_F('MaterialHistorySyncedTabsTest', 'DISABLED_All', function() {
+TEST_F('MaterialHistorySyncedTabsTest', 'All', function() {
   mocha.run();
 });
 
 function MaterialHistorySupervisedUserTest() {}
 
 MaterialHistorySupervisedUserTest.prototype = {
   __proto__: MaterialHistoryBrowserTest.prototype,
 
   typedefCppFixture: 'HistoryUIBrowserTest',
 
@@ skipping 22 matching lines @@
 
 TEST_F('MaterialHistoryToolbarTest', 'Basic', function() {
   md_history.history_toolbar_test.registerTests();
   mocha.run();
 });
 
 TEST_F('MaterialHistoryToolbarTest', 'Focus', function() {
   md_history.history_toolbar_focus_test.registerTests();
   mocha.run();
 });