Implement OffscreenCanvas.getContext('webgl')

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 55 matching lines @@
     static ContextType contextTypeFromId(const String& id);
     static ContextType resolveContextTypeAliases(ContextType);
 
     HTMLCanvasElement* canvas() const { return m_canvas; }
 
     virtual ContextType getContextType() const = 0;
     virtual bool isAccelerated() const { return false; }
     virtual bool hasAlpha() const { return true; }
     virtual void setIsHidden(bool) = 0;
     virtual bool isContextLost() const { return true; }
-    virtual void setCanvasGetContextResult(RenderingContext&) = 0;
+    virtual void setCanvasGetContextResult(RenderingContext&) { ASSERT_NOT_REACHED(); };
+    virtual void setOffscreenCanvasGetContextResult(OffscreenRenderingContext&) { ASSERT_NOT_REACHED(); }
 
     // Return true if the content is updated.
     virtual bool paintRenderingResultsToCanvas(SourceDrawingBuffer) { return false; }
 
     virtual WebLayer* platformLayer() const { return nullptr; }
 
     enum LostContextMode {
         NotLostContext,
 
         // Lost context occurred at the graphics system level.
@@ skipping 32 matching lines @@
     virtual bool paint(GraphicsContext&, const IntRect&) { return false; }
 
     bool wouldTaintOrigin(CanvasImageSource*);
     void didMoveToNewDocument(Document*);
 
     // OffscreenCanvas-specific methods
     OffscreenCanvas* getOffscreenCanvas() const { return m_offscreenCanvas; }
     virtual ImageBitmap* transferToImageBitmap(ExceptionState&) { return nullptr; }
 
 protected:
-    CanvasRenderingContext(HTMLCanvasElement*);
-    CanvasRenderingContext(OffscreenCanvas*);
+    CanvasRenderingContext(HTMLCanvasElement* = nullptr, OffscreenCanvas* = nullptr);
     DECLARE_VIRTUAL_TRACE();
     virtual void stop() = 0;
 
 private:
     Member<HTMLCanvasElement> m_canvas;
     Member<OffscreenCanvas> m_offscreenCanvas;
     HashSet<String> m_cleanURLs;
     HashSet<String> m_dirtyURLs;
 };
 
 } // namespace blink
 
 #endif