GraphicsContext culling support.

Source/platform/graphics/GraphicsContext.h

Index: Source/platform/graphics/GraphicsContext.h
diff --git a/Source/platform/graphics/GraphicsContext.h b/Source/platform/graphics/GraphicsContext.h
index 39b71b135504f703951f3164ade0fed0b08a5852..5dfcf7f0820ef4908c5b618f25550831f7facbc0 100644
--- a/Source/platform/graphics/GraphicsContext.h
+++ b/Source/platform/graphics/GraphicsContext.h
@@ -305,6 +305,9 @@ public:
     void beginLayer(float opacity, CompositeOperator, const FloatRect* = 0, ColorFilter = ColorFilterNone, ImageFilter* = 0);
     void endLayer();
 
+    void beginCull(const FloatRect&);
+    void endCull();
+
     // Instead of being dispatched to the active canvas, draw commands following beginRecording()
     // are stored in a display list that can be replayed at a later time.
     void beginRecording(const FloatRect& bounds);