[Extensions] More bindings hardening

chrome/renderer/resources/extensions/notifications_custom_bindings.js

 // Copyright 2013 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.
 
 // Custom bindings for the notifications API.
 //
 var binding = require('binding').Binding.create('notifications');
 
 var sendRequest = require('sendRequest').sendRequest;
 var exceptionHandler = require('uncaught_exception_handler');
@@ skipping 126 matching lines @@
                              function(callback, id) { callback(false); });
 
 var notificationsCustomHook = function(bindingsAPI, extensionId) {
   var apiFunctions = bindingsAPI.apiFunctions;
   apiFunctions.setHandleRequest('create', handleCreate);
   apiFunctions.setHandleRequest('update', handleUpdate);
 };
 
 binding.registerCustomHook(notificationsCustomHook);
 
-exports.binding = binding.generate();
+exports.$set('binding', binding.generate());