ntp4: fix app context menu z-order

chrome/browser/resources/bookmark_manager/js/main.js

 // Copyright (c) 2011 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.
 
 const BookmarkList = bmm.BookmarkList;
 const BookmarkTree = bmm.BookmarkTree;
 const ListItem = cr.ui.ListItem;
 const TreeItem = cr.ui.TreeItem;
 const LinkKind = cr.LinkKind;
 const Command = cr.ui.Command;
 const CommandBinding = cr.ui.CommandBinding;
 const Menu = cr.ui.Menu;
 const MenuButton  = cr.ui.MenuButton;
 const Promise = cr.Promise;
 
 // Sometimes the extension API is not initialized.
 if (!chrome.bookmarks)
   console.error('Bookmarks extension API is not available');
 
-// Allow platform specific CSS rules.
-if (cr.isMac)
-  document.documentElement.setAttribute('os', 'mac');
+cr.enablePlatformSpecificCSSRules();
 
 /**
  * The local strings object which is used to do the translation.
  * @type {!LocalStrings}
  */
 var localStrings = new LocalStrings;
 
 // Get the localized strings from the backend.
 chrome.experimental.bookmarkManager.getStrings(function(data) {
   // The strings may contain & which we need to strip.
@@ skipping 1582 matching lines @@
   document.addEventListener('copy', handle('copy-command'));
   document.addEventListener('cut', handle('cut-command'));
 
   var pasteHandler = handle('paste-command');
   document.addEventListener('paste', function(e) {
     // Paste is a bit special since we need to do an async call to see if we can
     // paste because the paste command might not be up to date.
     updatePasteCommand(pasteHandler);
   });
 })();