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

Source/modules/background_sync/PeriodicSyncEvent.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 PeriodicSyncEvent_h
 #define PeriodicSyncEvent_h
 
 #include "modules/EventModules.h"
 #include "modules/serviceworkers/ExtendableEvent.h"
 #include "wtf/text/AtomicString.h"
@@ skipping 12 matching lines @@
     }
     static PassRefPtrWillBeRawPtr<PeriodicSyncEvent> create(const AtomicString& type, PeriodicSyncRegistration* syncRegistration, WaitUntilObserver* observer)
     {
         return adoptRefWillBeNoop(new PeriodicSyncEvent(type, syncRegistration, observer));
     }
     static PassRefPtrWillBeRawPtr<PeriodicSyncEvent> create(const AtomicString& type, const PeriodicSyncEventInit& init)
     {
         return adoptRefWillBeNoop(new PeriodicSyncEvent(type, init));
     }
 
-    virtual ~PeriodicSyncEvent();
+    ~PeriodicSyncEvent() override;
 
-    virtual const AtomicString& interfaceName() const override;
+    const AtomicString& interfaceName() const override;
 
     PeriodicSyncRegistration* registration();
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     PeriodicSyncEvent();
     PeriodicSyncEvent(const AtomicString& type, PeriodicSyncRegistration*, WaitUntilObserver*);
     PeriodicSyncEvent(const AtomicString& type, const PeriodicSyncEventInit&);
 
     PersistentWillBeMember<PeriodicSyncRegistration> m_periodicRegistration;
 };
 
 } // namespace blink
 
 #endif // PeriodicSyncEvent_h