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 e50b22e5205e7f496382be7851be5b05eca1ee41..1b27cf2b10cdc58f2e74fdb796169a48a462c1eb 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
@@ -51,6 +51,7 @@
 #include "core/paint/PaintLayerFragment.h"
 #include "core/paint/ScrollbarManager.h"
 #include "platform/heap/Handle.h"
+#include "platform/scroll/MainThreadScrollingReason.h"
 #include "wtf/PtrUtil.h"
 #include <memory>
 
@@ -475,6 +476,11 @@ class CORE_EXPORT PaintLayerScrollableArea final
   void invalidateStickyConstraintsFor(PaintLayer*,
                                       bool needsCompositingUpdate = true);
 
+  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();
@@ -579,6 +585,9 @@ class CORE_EXPORT PaintLayerScrollableArea final
 
   std::unique_ptr<PaintLayerScrollableAreaRareData> m_rareData;
 
+  // MainThreadScrollingReason due to the property of each layout object
+  uint32_t m_reasons;
+
 #if ENABLE(ASSERT)
   bool m_hasBeenDisposed;
 #endif