Added menuItem icon support, and little API for menu modification.

chrome/browser/resources/shared/js/cr/ui/menu_item.js

 // Copyright (c) 2012 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.
 
 cr.define('cr.ui', function() {
   /** @const */ var Command = cr.ui.Command;
 
   /**
    * Creates a new menu item element.
    * @param {Object=} opt_propertyBag Optional properties.
@@ skipping 21 matching lines @@
     decorate: function() {
       var commandId;
       if ((commandId = this.getAttribute('command')))
         this.command = commandId;
 
       this.addEventListener('mouseup', this.handleMouseUp_);
 
       // Adding the 'custom-appearance' class prevents widgets.css from changing
       // the appearance of this element.
       this.classList.add('custom-appearance');
+
+      var iconUrl;
+      if ((iconUrl = this.getAttribute('icon')))
+        this.iconUrl = iconUrl;

[James Hawkins, 2012/05/16 17:12:18]

Why not:

this.iconUrl = this.getAttribute('icon');

?

[Dmitry Zvorygin, 2012/05/17 12:11:15]

We don't want to set iconUrl to 'undefined'. Just leave default if iconUrl isn't
specified.

     },
 
     /**
      * The command associated with this menu item. If this is set to a string
      * of the form "#element-id" then the element is looked up in the document
      * of the command.
      * @type {cr.ui.Command}
      */
     command_: null,
     get command() {
@@ skipping 33 matching lines @@
      * @type {string}
      */
     get label() {
       return this.textContent;
     },
     set label(label) {
       this.textContent = label;
     },
 
     /**
+     * Menu icon.
+     * @type {string}
+     */
+    get iconUrl() {
+      return this.style.backgroundImage;
+    },
+    set iconUrl(url) {
+      this.style.backgroundImage = 'url(' + url + ')';
+    },
+
+    /**
      * @return {boolean} Whether the menu item is a separator.
      */
     isSeparator: function() {
       return this.tagName == 'HR';
     },
 
     /**
      * Handles mouseup events. This dispatches an active event and if there
      * is an assiciated command then that is executed.
      * @param {Event} The mouseup event object.
@@ skipping 54 matching lines @@
    * Whether the menu item is checked or not.
    * @type {boolean}
    */
   cr.defineProperty(MenuItem, 'checked', cr.PropertyKind.BOOL_ATTR);
 
   // Export
   return {
     MenuItem: MenuItem
   };
 });