Canvas2d: Implement rerouting event by hit region's control.

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 91 matching lines @@
     // Canvas2D-specific interface
     virtual bool is2d() const { return false; }
     virtual void restoreCanvasMatrixClipStack(SkCanvas*) const { }
     virtual void reset() { }
     virtual void clearRect(double x, double y, double width, double height) { }
     virtual void didSetSurfaceSize() { }
     virtual void setShouldAntialias(bool) { }
     virtual unsigned hitRegionsCount() const { return 0; }
     virtual void setFont(const String&) { }
     virtual void styleDidChange(const ComputedStyle* oldStyle, const ComputedStyle& newStyle) { }
+    virtual std::pair<Element*, String> getControlAndIDIfHitRegionExists(const LayoutPoint& location) { return std::make_pair(nullptr, String()); }

[Justin Novosad, 2016/02/05 15:22:53]

I think this default implementation (and the all the other ones that should
never be invoked on a WebGL canvas) should have ASSERT_NOT_REACHED();  As was
done in the WebGL section below.

[zino, 2016/02/12 15:26:19]

Done.

 
     // WebGL-specific interface
     virtual bool is3d() const { return false; }
     virtual void setFilterQuality(SkFilterQuality) { ASSERT_NOT_REACHED(); }
     virtual void reshape(int width, int height) { ASSERT_NOT_REACHED(); }
     virtual void markLayerComposited() { ASSERT_NOT_REACHED(); }
     virtual ImageData* paintRenderingResultsToImageData(SourceDrawingBuffer) { ASSERT_NOT_REACHED(); return nullptr; }
     virtual int externallyAllocatedBytesPerPixel() { ASSERT_NOT_REACHED(); return 0; }
 
     bool wouldTaintOrigin(CanvasImageSource*);
     void didMoveToNewDocument(Document*);
 
 protected:
     CanvasRenderingContext(HTMLCanvasElement*);
     DECLARE_VIRTUAL_TRACE();
 
     // ActiveDOMObject notifications
     bool hasPendingActivity() const final;
     void stop() override = 0;
 
 private:
     RawPtrWillBeMember<HTMLCanvasElement> m_canvas;
     HashSet<String> m_cleanURLs;
     HashSet<String> m_dirtyURLs;
 };
 
 } // namespace blink
 
 #endif