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

Source/core/html/track/TrackListBase.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 TrackListBase_h
 #define TrackListBase_h
 
 #include "core/events/EventTarget.h"
 
 #include "core/html/HTMLMediaElement.h"
 #include "core/html/track/TrackEvent.h"
 #include "core/html/track/TrackEventInit.h"
 
 namespace blink {
 
 template<class T>
 class TrackListBase : public EventTargetWithInlineData, public RefCountedWillBeNoBase<TrackListBase<T>> {
     REFCOUNTED_EVENT_TARGET(TrackListBase);
 public:
     explicit TrackListBase(HTMLMediaElement* mediaElement)
         : m_mediaElement(mediaElement)
     {
     }
 
-    virtual ~TrackListBase()
+    ~TrackListBase() override
     {
 #if !ENABLE(OILPAN)
         ASSERT(m_tracks.isEmpty());
         ASSERT(!m_mediaElement);
 #endif
     }
 
     unsigned length() const { return m_tracks.size(); }
     T* anonymousIndexedGetter(unsigned index) const
     {
@@ skipping 10 matching lines @@
         }
 
         return nullptr;
     }
 
     DEFINE_ATTRIBUTE_EVENT_LISTENER(change);
     DEFINE_ATTRIBUTE_EVENT_LISTENER(addtrack);
     DEFINE_ATTRIBUTE_EVENT_LISTENER(removetrack);
 
     // EventTarget interface
-    virtual ExecutionContext* executionContext() const override
+    ExecutionContext* executionContext() const override
     {
         if (m_mediaElement)
             return m_mediaElement->executionContext();
         return nullptr;
     }
 
 #if !ENABLE(OILPAN)
     void shutdown()
     {
         removeAll();
@@ skipping 56 matching lines @@
         m_mediaElement->scheduleEvent(event);
     }
 
     WillBeHeapVector<RefPtrWillBeMember<T>> m_tracks;
     RawPtrWillBeMember<HTMLMediaElement> m_mediaElement;
 };
 
 } // namespace blink
 
 #endif