Add more specific metrics for main thread scrolling reasons

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
index ea237d5316e3f3947d011ec68a8134563df0cfb8..90326393c65c333abe3c840b2409acefe47672f1 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
@@ -474,6 +474,12 @@ class CORE_EXPORT PaintLayerScrollableArea final
   void invalidateStickyConstraintsFor(PaintLayer*,
                                       bool needsCompositingUpdate = true);
 
+  void updateMainThreadScrollingReasonsFromStyle(const PaintLayer*) const;
+  bool hasMainThreadScrollingReason(uint32_t reason) const {
+    return m_reasons & reason;
+  }
+  void flipMainThreadScrollingReason(uint32_t reason) { m_reasons ^= reason; }
+
   uint64_t id() const;
 
   DECLARE_VIRTUAL_TRACE();
@@ -578,6 +584,9 @@ class CORE_EXPORT PaintLayerScrollableArea final
 
   std::unique_ptr<PaintLayerScrollableAreaRareData> m_rareData;
 
+  // MainThreadScrollingReason due to the properties of the LayoutObject
+  uint32_t m_reasons;
+
 #if ENABLE(ASSERT)
   bool m_hasBeenDisposed;
 #endif