Add PushMessagingHasPermission runtime flag to expose PushManager.hasPermission()

Source/modules/push_messaging/PushManager.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/push-api/#pushmanager-interface
 
 [
     Exposed=(Window,ServiceWorker),
     GarbageCollected,
     RuntimeEnabled=PushMessaging,
 ] interface PushManager {
     [CallWith=ScriptState] Promise<PushSubscription> subscribe();
     [CallWith=ScriptState] Promise<PushSubscription?> getSubscription();
-    [CallWith=ScriptState] Promise hasPermission();
+    [RuntimeEnabled=PushMessagingHasPermission,CallWith=ScriptState] Promise hasPermission();
 };