Improve accessibility of user image selection screen.

chrome/browser/resources/shared/js/cr/ui/list_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() {
 
   /**
    * Creates a new list item element.
    * @param {string} opt_label The text label for the item.
    * @constructor
@@ skipping 18 matching lines @@
     /**
      * This item's index in the containing list.
      * @type {number}
      */
     listIndex_: -1,
 
     /**
      * Called when an element is decorated as a list item.
      */
     decorate: function() {
-      this.setAttribute('role', 'listitem');
+      this.setAttribute('role', 'option');
     },
 
     /**
      * Called when the selection state of this element changes.
      */
     selectionChanged: function() {
     },
   };
 
   /**
@@ skipping 16 matching lines @@
   /**
    * This item's index in the containing list.
    * @type {number}
    */
   cr.defineProperty(ListItem, 'listIndex');
 
   return {
     ListItem: ListItem
   };
 });