ServiceWorker: Update IDLs to use ScalarValueString

Source/modules/serviceworkers/Response.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#response-objects
+// http://fetch.spec.whatwg.org/#response-class
 // FIXME: Split this idl/impl into AbstractResponse and Response.
 [
     // FIXME: Add ctors for String, Stream, and ArrayBuffer/ArrayBufferView response bodies.
     Constructor(Blob body, optional Dictionary responseInitDict),
     RuntimeEnabled=ServiceWorker,
     Exposed=ServiceWorker
 ] interface Response {
     attribute unsigned short status;
     attribute ByteString statusText;
     readonly attribute HeaderMap headers;
 
     // FIXME: Implement the following:
     // attribute DOMString url;
     // Promise<Blob> toBlob();
 };