[Extensions] More bindings hardening

chrome/renderer/resources/extensions/sync_file_system_custom_bindings.js

 // Copyright (c) 2012 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 binding for the syncFileSystem API.
 
 var binding = require('binding').Binding.create('syncFileSystem');
 
 var eventBindings = require('event_bindings');
 var fileSystemNatives = requireNative('file_system_natives');
@@ skipping 86 matching lines @@
   var fileInfo = new Object();
   fileInfo.fileEntry = fileEntry;
   fileInfo.status = args[1];
   if (fileInfo.status == "synced") {
     fileInfo.action = args[2];
     fileInfo.direction = args[3];
   }
   dispatch([fileInfo]);
 });
 
-exports.binding = binding.generate();
+exports.$set('binding', binding.generate());