Implement "Save image as" for canvas (blink side).

Source/core/rendering/RenderHTMLCanvas.h

 /*
  * Copyright (C) 2004, 2006, 2007, 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 24 matching lines @@
 class RenderHTMLCanvas FINAL : public RenderReplaced {
 public:
     explicit RenderHTMLCanvas(HTMLCanvasElement*);
 
     virtual bool isCanvas() const OVERRIDE { return true; }
     virtual LayerType layerTypeRequired() const OVERRIDE;
 
     void canvasSizeChanged();
 
 private:
+    virtual bool isImage() const OVERRIDE { return true; }

[Justin Novosad, 2014/04/24 14:19:39]

This is not a good idea. It implies that the object is an HTML image, which it
is not.  Instead you should change the relevant call sites to (isImage() ||
isCanvas())

     virtual const char* renderName() const OVERRIDE { return "RenderHTMLCanvas"; }
     virtual void paintReplaced(PaintInfo&, const LayoutPoint&) OVERRIDE;
     virtual void intrinsicSizeChanged() OVERRIDE { canvasSizeChanged(); }
 
     virtual CompositingReasons additionalCompositingReasons(CompositingTriggerFlags) const OVERRIDE;
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderHTMLCanvas, isCanvas());
 
 } // namespace WebCore
 
 #endif // RenderHTMLCanvas_h