Pass data saver pref value into embedded worker

content/test/data/service_worker/add_save_data_to_title.js

Index: content/test/data/service_worker/add_save_data_to_title.js
diff --git a/content/test/data/service_worker/fetch_event_blob.js b/content/test/data/service_worker/add_save_data_to_title.js
similarity index 53%
copy from content/test/data/service_worker/fetch_event_blob.js
copy to content/test/data/service_worker/add_save_data_to_title.js
index 8f15e1f1235d0290346920fa79bbebefd9461a1f..7facfe5d21eef10a3418e480fee54850ce63eadb 100644
--- a/content/test/data/service_worker/fetch_event_blob.js
+++ b/content/test/data/service_worker/add_save_data_to_title.js
@@ -1,9 +1,10 @@
-// Copyright 2015 The Chromium Authors. All rights reserved.
+// Copyright 2016 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.
 
 this.onfetch = function(event) {
-    var blob = new Blob(['<title>Title</title>']);
+    var value = event.request.headers.get('Save-Data');
+    var blob = new Blob(['<title>save-data='+ value + '</title>']);
     var response = new Response(blob);
     event.respondWith(response);
 };