CacheStorage: Implement Cache.addAll() behind a flag

Source/modules/cachestorage/Cache.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.
 
 // See https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#cache
 
 [
     GarbageCollected,
     Exposed=(Window,Worker),
     RuntimeEnabled=ServiceWorkerCache,
     TypeChecking=Interface,
 ] interface Cache {
     [CallWith=ScriptState, RaisesException] Promise<Response> match(RequestInfo request, optional CacheQueryOptions options);
 
     // FIXME: Implement matchAll(): http://crbug.com/428363
     // FIXME: First argument of matchAll() should be optional: http://crbug.com/425459
     // [CallWith=ScriptState, RaisesException] Promise<sequence<Response>> matchAll(RequestInfo request, optional CacheQueryOptions options);
 
     [CallWith=ScriptState, RaisesException] Promise<void> add(RequestInfo request);
-
-    // FIXME: Implement addAll(): http://crbug.com/427652
-    // [CallWith=ScriptState] Promise<void> addAll(sequence<RequestInfo> requests);
-
+    [RuntimeEnabled=ServiceWorkerCacheAddAll, CallWith=ScriptState, RaisesException] Promise<void> addAll(sequence<RequestInfo> requests);
     [CallWith=ScriptState, RaisesException] Promise<void> put(RequestInfo request, Response response);
     [CallWith=ScriptState, ImplementedAs=deleteFunction, RaisesException] Promise<boolean> delete(RequestInfo request, optional CacheQueryOptions options);
     [CallWith=ScriptState, RaisesException] Promise<sequence<Response>> keys(optional RequestInfo request, optional CacheQueryOptions options);
 };