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 e2bd6492b516b30a3c4ee1d4128dcbb291e88ce7..f050067a87b37b17b57351561c08cdfc2043ca89 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
@@ -476,6 +476,14 @@ class CORE_EXPORT PaintLayerScrollableArea final
   void invalidateStickyConstraintsFor(PaintLayer*,
                                       bool needsCompositingUpdate = true);
 
+  void removeStyleRelatedMainThreadScrollingReasons();
+  void addStyleRelatedMainThreadScrollingReasons(const uint32_t);
+  bool hasMainThreadScrollingReason(uint32_t reason) const {
+    return m_reasons & reason;
+  }
+  void setMainThreadScrollingReason(uint32_t reason) { m_reasons |= reason; }

[bokan, 2016/12/20 19:35:53]

These aren't called from outside the class and only called in one place inside.
Remove the set and reset method and just inline the `|=` and `&=` inside
addStyle../removeStyle... where they're used.

[yigu, 2016/12/20 19:59:31]

Done.

+  void resetMainThreadScrollingReason(uint32_t reason) { m_reasons &= ~reason; }
+
   uint64_t id() const;
 
   DECLARE_VIRTUAL_TRACE();
@@ -531,6 +539,7 @@ class CORE_EXPORT PaintLayerScrollableArea final
     return *m_rareData.get();
   }
 
+  bool layerNeedsCompositedScrolling(const LCDTextMode, const PaintLayer*);
   PaintLayer& m_layer;
 
   PaintLayer* m_nextTopmostScrollChild;
@@ -582,6 +591,9 @@ 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