Implement convertToBlob() in OffscreenCanvas

third_party/WebKit/Source/core/html/canvas/CanvasRenderingContext.h

 /*
  * Copyright (C) 2009 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 70 matching lines @@
   static ContextType resolveContextTypeAliases(ContextType);
 
   HTMLCanvasElement* canvas() const { return m_canvas; }
 
   CanvasColorSpace colorSpace() const { return m_colorSpace; };
   WTF::String colorSpaceAsString() const;
   sk_sp<SkColorSpace> skColorSpace() const;
 
   virtual PassRefPtr<Image> getImage(AccelerationHint,
                                      SnapshotReason) const = 0;
+  virtual ImageData* toImageData(SnapshotReason reason) const {
+    return nullptr;
+  }
   virtual ContextType getContextType() const = 0;
   virtual bool isAccelerated() const { return false; }
   virtual bool shouldAntialias() const { return false; }
   virtual void setIsHidden(bool) = 0;
   virtual bool isContextLost() const { return true; }
   virtual void setCanvasGetContextResult(RenderingContext&) { NOTREACHED(); };
   virtual void setOffscreenCanvasGetContextResult(OffscreenRenderingContext&) {
     NOTREACHED();
   }
   virtual bool isPaintable() const = 0;
@@ skipping 86 matching lines @@
   Member<OffscreenCanvas> m_offscreenCanvas;
   HashSet<String> m_cleanURLs;
   HashSet<String> m_dirtyURLs;
   CanvasColorSpace m_colorSpace;
   CanvasContextCreationAttributes m_creationAttributes;
 };
 
 }  // namespace blink
 
 #endif