ServiceWorker: Read the blob from SW's response to a fetch event

content/test/data/service_worker/sync.js

 // Copyright 2014 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.
 
 var code = 404;
 
 this.onfetch = function(event) {
-    response = new Response({
+    response = new Response(new Blob(), {
         status: code,
         statusText: 'OK'
     });
 
     event.respondWith(new Promise(function(r) {
         setTimeout(function() { r(response); }, 5);
     }));
 };
 
 this.onsync = function(event) {
     code = 200;
 };