ServiceWorker: Spec alignment tweaks for Request/Response objects

Source/modules/serviceworkers/Request.idl

 // 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.
 
 // https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#request-objects
 
 [
     Constructor(optional Dictionary requestInitDict),
     RuntimeEnabled=ServiceWorker,
     Exposed=ServiceWorker
 ] interface Request {
     attribute DOMString url;
-    // FIXME: Spec uses ByteString for this. We must perform the DOMString -> ByteString conversion manually (crbug.com/347426).
-    attribute DOMString method;
+    attribute ByteString method;
     readonly attribute DOMString origin;
     readonly attribute HeaderMap headers;
 
     // FIXME: Implement the following:
     // attribute unsigned long timeout;
     // readonly attribute Mode mode;
     // attribute boolean synchronous;
     // readonly attribute unsigned long redirectCount;
     // attribute boolean forcePreflight;
     // attribute boolean forceSameOrigin;
     // attribute boolean omitCredentials;
     // readonly attribute DOMString referrer;
     // attribute any body;
 };