Add initial support for [Exposed=xx] extended IDL attribute

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.
 
 [
     Constructor(optional Dictionary responseInitDict),
     RuntimeEnabled=ServiceWorker,
-    GlobalContext=ServiceWorkerGlobalScope,
+    Exposed=ServiceWorker
 ] interface Response {
     attribute unsigned short statusCode;
 
     // FIXME: Spec uses ByteString for these. We must perform the DOMString -> ByteString conversion manually (crbug.com/347426).
     attribute DOMString statusText;
     attribute DOMString method;
 
     // FIXME: Implement HeaderMap which uses the MapClass WebIDL attribute (crbug.com/347435).
     getter Dictionary headers();
     setter void headers(Dictionary items);
 
     // FIXME: Implement the following:
     // attribute DOMString url;
     // Promise<Blob> toBlob();
 };