[Extensions Bindings] Include request id in a custom callback response

chrome/renderer/resources/extensions/page_capture_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 pageCapture API.
 
-var binding = require('binding').Binding.create('pageCapture');
+var binding = apiBridge || require('binding').Binding.create('pageCapture');
 
 var handleUncaughtException = require('uncaught_exception_handler').handle;
 var pageCaptureNatives = requireNative('page_capture');
 var CreateBlob = pageCaptureNatives.CreateBlob;
 var SendResponseAck = pageCaptureNatives.SendResponseAck;
 
 binding.registerCustomHook(function(bindingsAPI) {
   var apiFunctions = bindingsAPI.apiFunctions;
 
   apiFunctions.setCustomCallback('saveAsMHTML',
       function(name, request, callback, response) {
     if (response)
       response = CreateBlob(response.mhtmlFilePath, response.mhtmlFileLength);
 
     try {
       callback(response);
     } catch (e) {
       handleUncaughtException(
           'Error in chrome.pageCapture.saveAsMHTML callback', e, request.stack);
     } finally {
       // Notify the browser. Now that the blob is referenced from JavaScript,
       // the browser can drop its reference to it.
       SendResponseAck(request.id);
     }
   });
 });
 
-exports.$set('binding', binding.generate());
+if (!apiBridge)
+  exports.$set('binding', binding.generate());