ServiceWorker: Update IDLs to use ScalarValueString

Source/modules/serviceworkers/HeaderMap.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#header-map-interface
+// http://fetch.spec.whatwg.org/#headers-class
+// FIXME: Fetch spec has renamed this to just 'Headers'
 // FIXME: This should be defined as MapClass(DOMString, DOMString)
 // once binding code supports it (http://crbug.com/347435).
 [
     Constructor,
     RuntimeEnabled=ServiceWorker,
     Exposed=ServiceWorker
 ] interface HeaderMap {
     readonly attribute unsigned long size;
 
     // FIXME: Define keys, values, entries.
     // FIXME: Some of the method definitions (like set) don't strictly
     // follow the MapClass's ones (http://heycam.github.io/webidl/#MapClass),
     // as this is supposed to be a transient implementation until we have real
     // MapClass.
 
     void clear();
     [ImplementedAs=remove] boolean delete(DOMString key);
     DOMString get(DOMString key);
     boolean has(DOMString key);
     void set(DOMString key, DOMString value);
     void forEach(HeaderMapForEachCallback callback, optional any thisArg);
 };