Add more specific metrics for main thread scrolling reasons

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

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CompositingReasonFinder_h
 #define CompositingReasonFinder_h
 
 #include "core/layout/compositing/CompositingTriggers.h"
 #include "platform/graphics/CompositingReasons.h"
 #include "wtf/Allocator.h"
@@ skipping 14 matching lines @@
   explicit CompositingReasonFinder(LayoutView&);
 
   CompositingReasons potentialCompositingReasonsFromStyle(LayoutObject*) const;
   CompositingReasons directReasons(const PaintLayer*) const;
 
   void updateTriggers();
 
   bool hasOverflowScrollTrigger() const;
   bool requiresCompositingForScrollableFrame() const;
   bool requiresCompositingForAnimation(const ComputedStyle&) const;
+  void updateMainThreadScrollingReasonDueToLayoutObject(
+      const PaintLayer*) const;
 
  private:
   bool isMainFrame() const;
 
   CompositingReasons nonStyleDeterminedDirectReasons(const PaintLayer*) const;
 
   bool requiresCompositingForTransform(LayoutObject*) const;
   bool requiresCompositingForScrollDependentPosition(const PaintLayer*) const;
 
   LayoutView& m_layoutView;
   CompositingTriggerFlags m_compositingTriggers;
 };
 
 }  // namespace blink
 
 #endif  // CompositingReasonFinder_h