[ServiceWorker] Make fetch() method better conformance with the spec.

Source/modules/serviceworkers/ServiceWorkerGlobalScope.idl

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 23 matching lines @@
     Global=Worker&ServiceWorker,
     RuntimeEnabled=ServiceWorker,
 ] interface ServiceWorkerGlobalScope : WorkerGlobalScope {
 
   readonly attribute ServiceWorkerClients clients;
   [CallWith=ExecutionContext, Unforgeable] readonly attribute ScalarValueString scope;
 
   // FIXME: Rename to "caches" once native Cache API implementation is available.
   [CallWith=ExecutionContext, Unforgeable, ImplementedAs=caches] readonly attribute CacheStorage nativeCaches;
 
-  [CallWith=ScriptState] Promise fetch(ScalarValueString request);
-  [CallWith=ScriptState] Promise fetch(Request request);
+  [CallWith=ScriptState] Promise fetch(DOMString request, optional Dictionary requestInitDict);
+  [CallWith=ScriptState] Promise fetch(Request request, optional Dictionary requestInitDict);
 
   attribute EventHandler onactivate;
   attribute EventHandler onfetch;
   attribute EventHandler oninstall;
   attribute EventHandler onmessage;
   attribute EventHandler onsync;
 };