[Extensions] Don't allow built-in extensions code to be overridden

extensions/renderer/resources/messaging.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.
 
 // chrome.runtime.messaging API implementation.
 
   // TODO(kalman): factor requiring chrome out of here.
   var chrome = requireNative('chrome').GetChrome();
   var Event = require('event_bindings').Event;
   var lastError = require('lastError');
@@ skipping 359 matching lines @@
 var Port = utils.expose('Port', PortImpl, { functions: [
     'disconnect',
     'postMessage'
   ],
   properties: [
     'name',
     'onDisconnect',
     'onMessage'
   ] });
 
-exports.kRequestChannel = kRequestChannel;
-exports.kMessageChannel = kMessageChannel;
-exports.kNativeMessageChannel = kNativeMessageChannel;
-exports.Port = Port;
-exports.createPort = createPort;
-exports.sendMessageImpl = sendMessageImpl;
-exports.sendMessageUpdateArguments = sendMessageUpdateArguments;
+exports.$set('kRequestChannel', kRequestChannel);
+exports.$set('kMessageChannel', kMessageChannel);
+exports.$set('kNativeMessageChannel', kNativeMessageChannel);
+exports.$set('Port', Port);
+exports.$set('createPort', createPort);
+exports.$set('sendMessageImpl', sendMessageImpl);
+exports.$set('sendMessageUpdateArguments', sendMessageUpdateArguments);
 
 // For C++ code to call.
-exports.hasPort = hasPort;
-exports.dispatchOnConnect = dispatchOnConnect;
-exports.dispatchOnDisconnect = dispatchOnDisconnect;
-exports.dispatchOnMessage = dispatchOnMessage;
+exports.$set('hasPort', hasPort);
+exports.$set('dispatchOnConnect', dispatchOnConnect);
+exports.$set('dispatchOnDisconnect', dispatchOnDisconnect);
+exports.$set('dispatchOnMessage', dispatchOnMessage);