ServiceWorker: Implement ServiceWorkerRegistration [1/3]

Source/modules/serviceworkers/ServiceWorkerRegistration.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#service-worker-clients-interface
+// https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#service-worker-registration-obj
 [
-    Exposed=ServiceWorker,
+    ActiveDOMObject,
     RuntimeEnabled=ServiceWorker,
     WillBeGarbageCollected,
-] interface ServiceWorkerClients {
-    [CallWith=ScriptState] Promise getServiced();
+] interface ServiceWorkerRegistration : EventTarget {
+    readonly attribute ScalarValueString scope;
+
+    [CallWith=ScriptState] Promise unregister();
 };