Service Worker: Make ServiceWorkerRegistration.update() return a promise. (Blink 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-registration-obj
 [
     Exposed=(Window,Worker),
     ActiveDOMObject,
     GarbageCollected,
     TypeChecking=Interface,
 ] interface ServiceWorkerRegistration : EventTarget {
     [Unforgeable] readonly attribute ServiceWorker? installing;
     [Unforgeable] readonly attribute ServiceWorker? waiting;
     [Unforgeable] readonly attribute ServiceWorker? active;
 
     readonly attribute USVString scope;
 
-    [CallWith=ScriptState, RaisesException] void update();
+    [CallWith=ScriptState] Promise<void> update();
     [CallWith=ScriptState] Promise<boolean> unregister();
 
     attribute EventHandler onupdatefound;
 };