Make DisplayItemClient an interface

third_party/WebKit/Source/platform/DragImage.h

 /*
  * Copyright (C) 2007 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 50 matching lines @@
     float resolutionScale() const { return m_resolutionScale; }
     IntSize size() const { return IntSize(m_bitmap.width(), m_bitmap.height()); }
 
     void scale(float scaleX, float scaleY);
 
     static PassRefPtr<SkImage> resizeAndOrientImage(PassRefPtr<SkImage>, ImageOrientation, FloatSize imageScale = FloatSize(1, 1), float opacity = 1.0, InterpolationQuality = InterpolationNone);
 
 private:
     DragImage(const SkBitmap&, float resolutionScale, InterpolationQuality);
 
-    DisplayItemClient displayItemClient() const { return toDisplayItemClient(this); }
-
     SkBitmap m_bitmap;
     float m_resolutionScale;
     InterpolationQuality m_interpolationQuality;
 };
 
 }
 
 #endif // DragImage_h