DOMUI: Stub out List.activateItemAtIndex for lists that don't implement this

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

 // Copyright (c) 2010 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.
 
 // require: listselectionmodel.js
 
 /**
  * @fileoverview This implements a list control.
  */
 
@@ skipping 590 matching lines @@
     /**
      * Redraws a single item.
      * @param {number} index The row index to redraw.
      */
     redrawItem: function(index) {
       if (index >= this.firstIndex_ && index < this.lastIndex_) {
         delete this.cachedItems_[index];
         this.redraw();
       }
     },
+
+    /**
+     * Called when a list item is activated, currently only by a double click
+     * event.
+     * @param {number} index The index of the activated item.
+     */
+    activateItemAtIndex: function(index) {
+    },
   };
 
   cr.defineProperty(List, 'disabled', cr.PropertyKind.BOOL_ATTR);
 
   return {
     List: List
   }
 });