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

method.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/6203004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@71128 0039d316-1c4b-4281-b951-d872f2087c98

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

@@ -608,6 +608,14 @@ cr.define('cr.ui', function() {
         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);