[Merge to M59] Keep the wrapper of FetchEvent alive while waiting for the preload response.

third_party/WebKit/Source/modules/serviceworkers/FetchEvent.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://w3c.github.io/ServiceWorker/#fetch-event-interface
 [
+    ActiveScriptWrappable,
+    DependentLifetime,
     Constructor(DOMString type, FetchEventInit eventInitDict),
     ConstructorCallWith=ScriptState,
     Exposed=ServiceWorker,
 ] interface FetchEvent : ExtendableEvent {
     [SameObject] readonly attribute Request request;
     readonly attribute DOMString? clientId;
     readonly attribute boolean isReload;
 
     [CallWith=ScriptState, RaisesException] void respondWith(Promise<Response> r);
     [RuntimeEnabled=ServiceWorkerNavigationPreload, CallWith=ScriptState] readonly attribute Promise<any> preloadResponse;
 };