NOT FOR REVIEW - Update comp-scrolling state at a well defined point in the pipeline.

Source/core/rendering/RenderLayerCompositor.h

Index: Source/core/rendering/RenderLayerCompositor.h
diff --git a/Source/core/rendering/RenderLayerCompositor.h b/Source/core/rendering/RenderLayerCompositor.h
index a9579cba1a1ae1936d8dfe1d15da85e350d54e85..6963b1311e34d8e0a0752eb7eee2af996007ed2e 100644
--- a/Source/core/rendering/RenderLayerCompositor.h
+++ b/Source/core/rendering/RenderLayerCompositor.h
@@ -116,7 +116,12 @@ public:
 
     // Called when something outside WebKit affects the visible rect (e.g. delegated scrolling). Might schedule a layer flush.
     void didChangeVisibleRect();
-    
+   
+    // Iterates through the RenderLayer tree, if necessary, updating properties
+    // required for determining if compositing is necessary.
+    void updateCompositingRequirementsState(RenderLayer* updateRoot = 0);
+    void setNeedsUpdateCompositingRequirementsState(bool needsUpdate = true) { m_needsUpdateCompositingRequirementsState = needsUpdate; }
+
     // Rebuild the tree of compositing layers
     void updateCompositingLayers(CompositingUpdateType, RenderLayer* updateRoot = 0);
     
@@ -350,6 +355,7 @@ private:
     bool m_compositingLayersNeedRebuild;
     bool m_forceCompositingMode;
     bool m_inPostLayoutUpdate; // true when it's OK to trust layout information (e.g. layer sizes and positions)
+    bool m_needsUpdateCompositingRequirementsState;
 
     bool m_isTrackingRepaints; // Used for testing.