Drop unused showingTrackWithSameKind declaration from HTMLMediaElement

Source/core/html/HTMLMediaElement.h

 /*
  * Copyright (C) 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 363 matching lines @@
     void mediaLoadingFailed(WebMediaPlayer::NetworkState);
 
     // deferred loading (preload=none)
     bool loadIsDeferred() const;
     void deferLoad();
     void cancelDeferredLoad();
     void startDeferredLoad();
     void executeDeferredLoad();
     void deferredLoadTimerFired(Timer<HTMLMediaElement>*);
 
-    HTMLTrackElement* showingTrackWithSameKind(HTMLTrackElement*) const;
-
     void markCaptionAndSubtitleTracksAsUnconfigured();
 
     // This does not check user gesture restrictions.
     void playInternal();
 
     void gesturelessInitialPlayHalted();
     void autoplayMediaEncountered();
     void allowVideoRendering();
 
     void updateVolume();
@@ skipping 230 matching lines @@
 inline bool isHTMLMediaElement(const HTMLElement& element)
 {
     return isHTMLAudioElement(element) || isHTMLVideoElement(element);
 }
 
 DEFINE_HTMLELEMENT_TYPE_CASTS_WITH_FUNCTION(HTMLMediaElement);
 
 } // namespace blink
 
 #endif // HTMLMediaElement_h