[Extensions] More bindings hardening

chrome/renderer/resources/extensions/notifications_test_util.js

 // Copyright 2014 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.
 
 // NotificationsTestUtil contains stubs for the global classes and
 // variables used by notifications_custom_bindings.js that are not
 // available with gtestjs tests.
 var require = function(library) {
   return {
     binding: {
@@ skipping 20 matching lines @@
           scaleFactor: 0,
           icon: { width: 0, height: 0 },
           image: { width: 0, height: 0 },
           buttonIcon: { width: 0, height: 0}
         };
       }
     }
   }[library];
 }
 
-var exports = {};
+var exports = {
+  $set: function(k, v) { this.k = v; }
+};
 
 var $Array = {
   push: function (ary, val) {
     ary.push(val);
   }
 };
 
 var $Function = {
   bind: function (fn, context) {
     return fn.bind(context);
   }
 };