[Background Sync] Align exposed API with spec

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

 // 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.
 
 #ifndef SyncEvent_h
 #define SyncEvent_h
 
 #include "modules/EventModules.h"
 #include "modules/background_sync/SyncEventInit.h"
 #include "modules/background_sync/SyncRegistration.h"
 #include "modules/serviceworkers/ExtendableEvent.h"
 #include "platform/heap/Handle.h"
 #include "wtf/text/AtomicString.h"
 #include "wtf/text/WTFString.h"
 
 namespace blink {
 
 class MODULES_EXPORT SyncEvent final : public ExtendableEvent {
     DEFINE_WRAPPERTYPEINFO();
 public:
     static PassRefPtrWillBeRawPtr<SyncEvent> create()
     {
         return adoptRefWillBeNoop(new SyncEvent);
     }
-    static PassRefPtrWillBeRawPtr<SyncEvent> create(const AtomicString& type, SyncRegistration* syncRegistration, bool lastChance, WaitUntilObserver* observer)
+    static PassRefPtrWillBeRawPtr<SyncEvent> create(const AtomicString& type, const String& tag, bool lastChance, WaitUntilObserver* observer)
     {
-        return adoptRefWillBeNoop(new SyncEvent(type, syncRegistration, lastChance, observer));
+        return adoptRefWillBeNoop(new SyncEvent(type, tag, lastChance, observer));
     }
     static PassRefPtrWillBeRawPtr<SyncEvent> create(const AtomicString& type, const SyncEventInit& init)
     {
         return adoptRefWillBeNoop(new SyncEvent(type, init));
     }
 
     ~SyncEvent() override;
 
     const AtomicString& interfaceName() const override;
 
-    SyncRegistration* registration();
+    String tag();
     bool lastChance();
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     SyncEvent();
-    SyncEvent(const AtomicString& type, SyncRegistration*, bool, WaitUntilObserver*);
+    SyncEvent(const AtomicString& type, const String&, bool, WaitUntilObserver*);
     SyncEvent(const AtomicString& type, const SyncEventInit&);
 
-    PersistentWillBeMember<SyncRegistration> m_syncRegistration;
+    String m_tag;
     bool m_lastChance;
 };
 
 } // namespace blink
 
 #endif // SyncEvent_h