Clean up around text track display state updates

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 130 matching lines @@
     virtual String toString() const override;
 #endif
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     VTTCue(Document&, double startTime, double endTime, const String& text);
 
     Document& document() const;
 
-    VTTCueBox& ensureDisplayTree();
     PassRefPtrWillBeRawPtr<VTTCueBox> getDisplayTree();
 
     virtual void cueDidChange() override;
 
     void createVTTNodeTree();
     void copyVTTNodeToDOMTree(ContainerNode* vttNode, ContainerNode* root);
 
     bool lineIsAuto() const;
     bool textPositionIsAuto() const;
 
@@ skipping 27 matching lines @@
     bool m_snapToLines : 1;
     bool m_displayTreeShouldChange : 1;
 };
 
 // VTTCue is currently the only TextTrackCue subclass.
 DEFINE_TYPE_CASTS(VTTCue, TextTrackCue, cue, true, true);
 
 } // namespace blink
 
 #endif // VTTCue_h