Removing getBackingTextureImage from ImageBufferSurface

Source/platform/graphics/ImageBufferSurface.h

 /*
  * Copyright (c) 2013, Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 64 matching lines @@
     virtual void setFilterQuality(SkFilterQuality) { }
     virtual void setIsHidden(bool) { }
     virtual void setImageBuffer(ImageBuffer*) { }
     virtual PassRefPtr<SkPicture> getPicture();
     virtual void finalizeFrame(const FloatRect &dirtyRect) { }
     virtual void willDrawVideo() { }
     virtual void willOverwriteCanvas() { }
     virtual void draw(GraphicsContext*, const FloatRect& destRect, const FloatRect& srcRect, SkXfermode::Mode);
     virtual void setHasExpensiveOp() { }
 
-    // These methods return an SkImage representing the backing texture. We support both variants
-    // to avoid the snapshot overhead (flushing deferred draws, COW semantics, fallback in
-    // RecordingImageBufferSurface) when not strictly required.
-    virtual PassRefPtr<SkImage> newImageSnapshot() const { return nullptr; }
-    virtual PassRefPtr<SkImage> getBackingTextureImage() const { return nullptr; }
+    // May return nullptr if the surface is GPU-backed and the GPU context was lost.
+    virtual PassRefPtr<SkImage> newImageSnapshot() const = 0;
 
     OpacityMode opacityMode() const { return m_opacityMode; }
     const IntSize& size() const { return m_size; }
     void notifyIsValidChanged(bool isValid) const;
 
 protected:
     ImageBufferSurface(const IntSize&, OpacityMode);
     void clear();
 
 private:
     OpacityMode m_opacityMode;
     IntSize m_size;
 };
 
 } // namespace blink
 
 #endif