Fix virtual/override/final usage in Source/modules/.

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"
@@ skipping 13 matching lines @@
     }
     static PassRefPtrWillBeRawPtr<SyncEvent> create(const AtomicString& type, SyncRegistration* syncRegistration, WaitUntilObserver* observer)
     {
         return adoptRefWillBeNoop(new SyncEvent(type, syncRegistration, observer));
     }
     static PassRefPtrWillBeRawPtr<SyncEvent> create(const AtomicString& type, const SyncEventInit& init)
     {
         return adoptRefWillBeNoop(new SyncEvent(type, init));
     }
 
-    virtual ~SyncEvent();
+    ~SyncEvent() override;
 
-    virtual const AtomicString& interfaceName() const override;
+    const AtomicString& interfaceName() const override;
 
     SyncRegistration* registration();
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     SyncEvent();
     SyncEvent(const AtomicString& type, SyncRegistration*, WaitUntilObserver*);
     SyncEvent(const AtomicString& type, const SyncEventInit&);
 
     PersistentWillBeMember<SyncRegistration> m_syncRegistration;
 };
 
 } // namespace blink
 
 #endif // SyncEvent_h