Throttle prepaints to avoid colliding with post-load work

cc/layer_tree_host.h

Index: cc/layer_tree_host.h
diff --git a/cc/layer_tree_host.h b/cc/layer_tree_host.h
index c80e79d019e081e833e2f999b83c401e33828c81..88f625e054bb8edf8a3bfc48867fbfe6521f1347 100644
--- a/cc/layer_tree_host.h
+++ b/cc/layer_tree_host.h
@@ -9,6 +9,7 @@
 
 #include "IntRect.h"
 #include "base/basictypes.h"
+#include "base/cancelable_callback.h"
 #include "base/hash_tables.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
@@ -218,6 +219,7 @@ private:
     bool paintMasksForRenderSurface(Layer*, TextureUpdateQueue&);
 
     void updateLayers(Layer*, TextureUpdateQueue&);
+    void triggerPrepaint();
 
     void prioritizeTextures(const LayerList&, OverdrawMetrics&); 
     void setPrioritiesForSurfaces(size_t surfaceMemoryBytes);
@@ -231,6 +233,8 @@ private:
     bool m_animating;
     bool m_needsAnimateLayers;
 
+    base::CancelableClosure m_prepaintCallback;
+
     LayerTreeHostClient* m_client;
 
     int m_commitNumber;