[Extensions] More bindings hardening

chrome/renderer/resources/extensions/file_manager_private_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 fileManagerPrivate API.
 
 // Bindings
 var binding = require('binding').Binding.create('fileManagerPrivate');
 var eventBindings = require('event_bindings');
 
@@ skipping 187 matching lines @@
   });
 });
 
 eventBindings.registerArgumentMassager(
     'fileManagerPrivate.onDirectoryChanged', function(args, dispatch) {
   // Convert the entry arguments into a real Entry object.
   args[0].entry = GetExternalFileEntry(args[0].entry);
   dispatch(args);
 });
 
-exports.binding = binding.generate();
+exports.$set('binding', binding.generate());