[Extensions] More bindings hardening

chrome/renderer/resources/extensions/tts_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 tts API.
 
 var binding = require('binding').Binding.create('tts');
 
 var idGenerator = requireNative('id_generator');
 var sendRequest = require('sendRequest').sendRequest;
@@ skipping 36 matching lines @@
       handlers[id] = args[1].onEvent;
       // Keep the page alive until the event finishes.
       // Balanced in eventHandler.
       lazyBG.IncrementKeepaliveCount();
     }
     sendRequest(this.name, args, this.definition.parameters);
     return id;
   });
 });
 
-exports.binding = binding.generate();
+exports.$set('binding', binding.generate());