[Extensions] More bindings hardening

chrome/renderer/resources/extensions/web_view/chrome_web_view_internal_custom_bindings.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.
 
 var binding = require('binding').Binding.create('chromeWebViewInternal');
 var contextMenusHandlers = require('contextMenusHandlers');
 
 binding.registerCustomHook(function(bindingsAPI) {
   var apiFunctions = bindingsAPI.apiFunctions;
 
   var handlers = contextMenusHandlers.create(true /* isWebview */);
 
   apiFunctions.setHandleRequest('contextMenusCreate',
       handlers.requestHandlers.create);
 
   apiFunctions.setCustomCallback('contextMenusCreate',
       handlers.callbacks.create);
 
   apiFunctions.setCustomCallback('contextMenusUpdate',
       handlers.callbacks.update);
 
   apiFunctions.setCustomCallback('contextMenusRemove',
       handlers.callbacks.remove);
 
   apiFunctions.setCustomCallback('contextMenusRemoveAll',
       handlers.callbacks.removeAll);
 
 });
 
-exports.ChromeWebView = binding.generate();
+exports.$set('ChromeWebView', binding.generate());