Implement interest rects for synchronized paint.

third_party/WebKit/Source/platform/graphics/GraphicsLayerClient.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 50 matching lines @@
 class PLATFORM_EXPORT GraphicsLayerClient {
 public:
     virtual ~GraphicsLayerClient() {}
 
     // Callback for when compositor animation started.
     virtual void notifyAnimationStarted(const GraphicsLayer*, double monotonicTime, int group) { }
 
     virtual void notifyTextPainted() { }
 
     virtual void paintContents(const GraphicsLayer*, GraphicsContext&, GraphicsLayerPaintingPhase, const IntRect& inClip) const = 0;
+    // Paints the content if required, either because the content changed or its interest rect has too much unpainted area.
+    virtual void paintContentsIfNeeded(const GraphicsLayer*, GraphicsContext&, GraphicsLayerPaintingPhase) const = 0;
     virtual bool isTrackingPaintInvalidations() const { return false; }
 
     virtual String debugName(const GraphicsLayer*) = 0;
 
 #if ENABLE(ASSERT)
     // CompositedLayerMapping overrides this to verify that it is not
     // currently painting contents. An ASSERT fails, if it is.
     // This is executed in GraphicsLayer construction and destruction
     // to verify that we don't create or destroy GraphicsLayers
     // while painting.
     virtual void verifyNotPainting() { }
 #endif
 };
 
 } // namespace blink
 
 #endif // GraphicsLayerClient_h