[MD Bookmarks] Make disabled buttons in context menu do nothing when clicked.

chrome/browser/resources/md_bookmarks/command_manager.js

 // Copyright 2017 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 Element which shows context menus and handles keyboard
  * shortcuts.
  */
 cr.define('bookmarks', function() {
 
@@ skipping 441 matching lines @@
       } else {
         this.openCommandMenuAtPosition(e.detail.x, e.detail.y);
       }
     },
 
     /**
      * @param {Event} e
      * @private
      */
     onCommandClick_: function(e) {
+      if (e.currentTarget.getAttribute('disabled') != null)
+        return;
+
       this.handle(
           e.currentTarget.getAttribute('command'), assert(this.menuIds_));
       this.closeCommandMenu();
     },
 
     /**
      * @param {!Event} e
      * @private
      */
     onKeydown_: function(e) {
@@ skipping 112 matching lines @@
 
   /** @return {!bookmarks.CommandManager} */
   CommandManager.getInstance = function() {
     return assert(CommandManager.instance_);
   };
 
   return {
     CommandManager: CommandManager,
   };
 });