Implement a module system for the extension bindings JS.

chrome/renderer/resources/extensions/tts_engine_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 bindings for the ttsEngine API.
 
 (function() {
 
-native function GetChromeHidden();
+var chromeHidden = requireNative('chrome_hidden').GetChromeHidden();
 
-GetChromeHidden().registerCustomHook('ttsEngine', function() {
+chromeHidden.registerCustomHook('ttsEngine', function() {
   chrome.ttsEngine.onSpeak.dispatch = function(text, options, requestId) {
     var sendTtsEvent = function(event) {
       chrome.ttsEngine.sendTtsEvent(requestId, event);
     };
     chrome.Event.prototype.dispatch.apply(
         this, [text, options, sendTtsEvent]);
   };
 });
 
 })();