Fix virtual/override/final usage in Source/core/html/.

Source/core/html/track/AudioTrackList.h

 // Copyright 2014 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 AudioTrackList_h
 #define AudioTrackList_h
 
 #include "core/html/track/AudioTrack.h"
 #include "core/html/track/TrackListBase.h"
 
 namespace blink {
 
 class AudioTrackList final : public TrackListBase<AudioTrack> {
     DEFINE_WRAPPERTYPEINFO();
 public:
     static PassRefPtrWillBeRawPtr<AudioTrackList> create(HTMLMediaElement&);
 
-    virtual ~AudioTrackList();
+    ~AudioTrackList() override;
 
     bool hasEnabledTrack() const;
 
     // EventTarget
-    virtual const AtomicString& interfaceName() const override;
+    const AtomicString& interfaceName() const override;
 
 private:
     explicit AudioTrackList(HTMLMediaElement&);
 };
 
 } // namespace blink
 
 #endif // AudioTrackList_h