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

extensions/renderer/resources/send_request.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 exceptionHandler = require('uncaught_exception_handler');
 var lastError = require('lastError');
 var logging = requireNative('logging');
 var natives = requireNative('sendRequest');
 var validate = require('schemaUtils').validate;
 
@@ skipping 122 matching lines @@
 }
 
 function getCalledSendRequest() {
   return calledSendRequest;
 }
 
 function clearCalledSendRequest() {
   calledSendRequest = false;
 }
 
-exports.sendRequest = sendRequest;
-exports.getCalledSendRequest = getCalledSendRequest;
-exports.clearCalledSendRequest = clearCalledSendRequest;
-exports.safeCallbackApply = safeCallbackApply;
+exports.$set('sendRequest', sendRequest);
+exports.$set('getCalledSendRequest', getCalledSendRequest);
+exports.$set('clearCalledSendRequest', clearCalledSendRequest);
+exports.$set('safeCallbackApply', safeCallbackApply);
 
 // Called by C++.
-exports.handleResponse = handleResponse;
+exports.$set('handleResponse', handleResponse);