[Extensions] More bindings hardening

chrome/renderer/resources/extensions/cast_streaming_rtp_stream_custom_bindings.js

 // Copyright 2013 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 Cast Streaming RtpStream API.
 
 var binding = require('binding').Binding.create('cast.streaming.rtpStream');
 var natives = requireNative('cast_streaming_natives');
 
 binding.registerCustomHook(function(bindingsAPI, extensionId) {
@@ skipping 22 matching lines @@
   apiFunctions.setHandleRequest('getRawEvents',
       function(transportId, extraData, callback) {
         natives.GetRawEvents(transportId, extraData, callback);
   });
   apiFunctions.setHandleRequest('getStats',
       function(transportId, callback) {
         natives.GetStats(transportId, callback);
   });
 });
 
-exports.binding = binding.generate();
+exports.$set('binding', binding.generate());