Implement interest rects for synchronized paint.

third_party/WebKit/Source/platform/graphics/ContentLayerDelegate.h

 /*
  * Copyright (C) 2012 Google 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 @@
 
 namespace blink {
 
 class DisplayItemList;
 class GraphicsContext;
 class IntRect;
 
 class PLATFORM_EXPORT GraphicsContextPainter {
 public:
     virtual void paint(GraphicsContext&, const IntRect& clip) = 0;
+    // Paints the content if required, either because the content changed or its interest rect has too much unpainted area.
+    virtual void paintIfNeeded(GraphicsContext&) = 0;
     virtual DisplayItemList* displayItemList() = 0;
 
 protected:
     virtual ~GraphicsContextPainter() { }
 };
 
 class PLATFORM_EXPORT ContentLayerDelegate : public WebContentLayerClient {
     WTF_MAKE_NONCOPYABLE(ContentLayerDelegate);
 
 public:
     explicit ContentLayerDelegate(GraphicsContextPainter*);
     ~ContentLayerDelegate() override;
 
     // WebContentLayerClient implementation.
     void paintContents(SkCanvas*, const WebRect& clip, WebContentLayerClient::PaintingControlSetting = PaintDefaultBehavior) override;
     void paintContents(WebDisplayItemList*, const WebRect& clip, WebContentLayerClient::PaintingControlSetting = PaintDefaultBehavior) override;
     size_t approximateUnsharedMemoryUsage() const override;
 
 private:
     GraphicsContextPainter* m_painter;
 };
 
 } // namespace blink
 
 #endif // ContentLayerDelegate_h