[Background Sync] Converting Blink code to the MVP API

Source/modules/background_sync/SyncManager.idl

 // Copyright 2015 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.
 
+enum SyncPermissionState {
+  "default",
+  "denied",
+  "granted"
+};
+
 [
     Exposed=(Window,ServiceWorker),
     GarbageCollected,
     RuntimeEnabled=BackgroundSync,
     TypeChecking=Interface,
 ] interface SyncManager {
-    [CallWith=ScriptState,ImplementedAs=registerFunction] Promise<SyncRegistration> register(optional SyncRegistrationOptions options);
-    [CallWith=ScriptState] Promise<SyncRegistration> getRegistration(DOMString id);
-    [CallWith=ScriptState] Promise<sequence<SyncRegistration>> getRegistrations();
-    readonly attribute unsigned long minAllowablePeriod;
+    [CallWith=ScriptState,ImplementedAs=registerFunction] Promise<SyncRegistration> register([RuntimeEnabled=BackgroundSyncV2] optional SyncRegistrationOptions options);
+    [RuntimeEnabled=BackgroundSyncV2, CallWith=ScriptState] Promise<SyncRegistration> getRegistration(DOMString tag);
+    [RuntimeEnabled=BackgroundSyncV2, CallWith=ScriptState] Promise<sequence<SyncRegistration>> getRegistrations();
+    [RuntimeEnabled=BackgroundSyncV2, CallWith=ScriptState] Promise<SyncPermissionState> permissionState();
 };