[Extensions] More bindings hardening

chrome/renderer/resources/extensions/file_entry_binding_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.
 
 var fileSystemNatives = requireNative('file_system_natives');
 var GetIsolatedFileSystem = fileSystemNatives.GetIsolatedFileSystem;
 var sendRequest = require('sendRequest');
 var lastError = require('lastError');
 var GetModuleSystem = requireNative('v8_context').GetModuleSystem;
 // TODO(sammc): Don't require extension. See http://crbug.com/235689.
@@ skipping 100 matching lines @@
     // requireNative is only allowed while lazily loading an API.
     backgroundPage.chrome.fileSystem;
     var bindFileEntryCallback = backgroundPageModuleSystem.require(
         apiName).bindFileEntryCallback;
     var entryIdManager = backgroundPageModuleSystem.require('entryIdManager');
   }
   return {bindFileEntryCallback: bindFileEntryCallback,
           entryIdManager: entryIdManager};
 }
 
-exports.getFileBindingsForApi = getFileBindingsForApi;
+exports.$set('getFileBindingsForApi', getFileBindingsForApi);