Tweak TextTrackCue/VTTCue virtual functions

Source/core/html/track/vtt/VTTCue.h

 /*
  * Copyright (c) 2013, Opera Software ASA. 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 114 matching lines @@
         Middle,
         End,
         Left,
         Right,
         NumberOfAlignments
     };
     CueAlignment getAlignment() const { return m_cueAlignment; }
 
     virtual ExecutionContext* executionContext() const OVERRIDE;
 
-    virtual String toString() const;
+#ifndef NDEBUG
+    virtual String toString() const OVERRIDE;
+#endif
 
 private:
     VTTCue(Document&, double startTime, double endTime, const String& text);
 
     Document& document() const;
 
     PassRefPtr<VTTCueBox> displayTreeInternal();
     PassRefPtr<VTTCueBox> getDisplayTree(const IntSize& videoSize);
 
     virtual void cueDidChange() OVERRIDE;
@@ skipping 44 matching lines @@
 
 inline VTTCue* toVTTCue(TextTrackCue* cue)
 {
     // VTTCue is currently the only TextTrackCue subclass.
     return static_cast<VTTCue*>(cue);
 }
 
 } // namespace WebCore
 
 #endif