Make OffscreenCanvasRenderingContext2D renderable on a worker

third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef OffscreenCanvasRenderingContext2D_h
 #define OffscreenCanvasRenderingContext2D_h
 
 #include "core/html/canvas/CanvasContextCreationAttributes.h"
 #include "modules/canvas2d/BaseRenderingContext2D.h"
 #include "modules/offscreencanvas/OffscreenCanvasRenderingContext.h"
@@ skipping 49 matching lines @@
     void didDraw(const SkIRect& dirtyRect) final;
 
     bool stateHasFilter() final;
     SkImageFilter* stateGetFilter() final;
 
     void validateStateStack() final;
 
     bool hasAlpha() const override { return m_hasAlpha; }
     bool isContextLost() const override;
 
+    PassRefPtrWillBeRawPtr<ImageBitmap> transferToImageBitmap(ExceptionState&) final;
+
 protected:
     OffscreenCanvasRenderingContext2D(OffscreenCanvas*, const CanvasContextCreationAttributes& attrs);
     DECLARE_VIRTUAL_TRACE();
 
 private:
     bool m_hasAlpha;
+    bool m_originClean = true;
+    OwnPtr<ImageBuffer> m_imageBuffer;
 };
 
 } // namespace blink
 
 #endif // OffscreenCanvasRenderingContext2D_h