[Background Sync] Align exposed API with spec

third_party/WebKit/Source/modules/background_sync/SyncEvent.cpp

 // 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.
 
 #include "config.h"
 #include "modules/background_sync/SyncEvent.h"
 
 namespace blink {
 
 SyncEvent::SyncEvent()
 {
 }
 
-SyncEvent::SyncEvent(const AtomicString& type, SyncRegistration* syncRegistration, bool lastChance, WaitUntilObserver* observer)
+SyncEvent::SyncEvent(const AtomicString& type, const String& tag, bool lastChance, WaitUntilObserver* observer)
     : ExtendableEvent(type, ExtendableEventInit(), observer)
-    , m_syncRegistration(syncRegistration)
+    , m_tag(tag)
     , m_lastChance(lastChance)
 {
 }
 
 SyncEvent::SyncEvent(const AtomicString& type, const SyncEventInit& init)
     : ExtendableEvent(type, init)
 {
-    m_syncRegistration = init.registration();
+    m_tag = init.tag();
     m_lastChance = init.lastChance();
 }
 
 SyncEvent::~SyncEvent()
 {
 }
 
 const AtomicString& SyncEvent::interfaceName() const
 {
     return EventNames::SyncEvent;
 }
 
-SyncRegistration* SyncEvent::registration()
+String SyncEvent::tag()
 {
-    return m_syncRegistration.get();
+    return m_tag;
 }
 
 bool SyncEvent::lastChance()
 {
     return m_lastChance;
 }
 
 DEFINE_TRACE(SyncEvent)
 {
-    visitor->trace(m_syncRegistration);
     ExtendableEvent::trace(visitor);
 }
 
 } // namespace blink