Add more specific metrics for main thread scrolling reasons

third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.h

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2014 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
@@ skipping 39 matching lines @@
   //  For the z-order children of a compositing layer:
   //      If a child layers has a compositing layer, then all subsequent layers
   //      must be compositing in order to render above that layer.
   //
   //      If a child in the negative z-order list is compositing, then the layer
   //      itself must be compositing so that its contents render over that
   //      child.  This implies that its positive z-index children must also be
   //      compositing.
   //
   void update(PaintLayer* root);
+  void updateMainThreadScrollingReasonsFromStyle(const PaintLayer*) const;
 
  private:
   class OverlapMap;
   class RecursionData;
 
   void updateRecursive(PaintLayer* ancestorLayer,
                        PaintLayer* currentLayer,
                        OverlapMap&,
                        RecursionData&,
                        bool& descendantHas3DTransform,
                        Vector<PaintLayer*>& unclippedDescendants,
                        IntRect& absoluteDescendantBoundingBox);
 
   LayoutView& m_layoutView;
   CompositingReasonFinder& m_compositingReasonFinder;
 };
 
 }  // namespace blink
 
 #endif  // CompositingRequirementsUpdater_h