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

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

Index: chrome/browser/resources/shared/js/cr/ui/list.js
diff --git a/chrome/browser/resources/shared/js/cr/ui/list.js b/chrome/browser/resources/shared/js/cr/ui/list.js
index 6fbe1cce845d03ebb90c21dc00a833f521360bbd..ba1da003980f76ffe81acf3a0355f3e0699bcf72 100644
--- a/chrome/browser/resources/shared/js/cr/ui/list.js
+++ b/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);