Add a runtime enabled feature for Service Workers' Cache API.

Source/modules/serviceworkers/ServiceWorkerGlobalScope.idl

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 19 matching lines @@
 
 // https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#service-worker-global-scope-interface
 [
     Exposed=ServiceWorker,
     Global=(Worker,ServiceWorker),
     RuntimeEnabled=ServiceWorker,
 ] interface ServiceWorkerGlobalScope : WorkerGlobalScope {
 
   readonly attribute ServiceWorkerClients clients;
   [CallWith=ExecutionContext, Unforgeable] readonly attribute ScalarValueString scope;
-  [CallWith=ExecutionContext, Unforgeable, RuntimeEnabled=ServiceWorkerOnFetch] readonly attribute CacheStorage caches;
+  [CallWith=ExecutionContext, Unforgeable, RuntimeEnabled=ServiceWorkerCache] readonly attribute CacheStorage caches;
 
   [CallWith=ScriptState] Promise fetch(DOMString request, optional Dictionary requestInitDict);
   [CallWith=ScriptState] Promise fetch(Request request, optional Dictionary requestInitDict);
 
   [RaisesException] void close();
 
   attribute EventHandler onactivate;
   [RuntimeEnabled=ServiceWorkerOnFetch] attribute EventHandler onfetch;
   attribute EventHandler oninstall;
   attribute EventHandler onmessage;
   [RuntimeEnabled=BackgroundSync] attribute EventHandler onsync;
 };