Add more specific metrics for main thread scrolling reasons

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

 /*
  * Copyright (C) 2003, 2009, 2012 Apple Inc. All rights reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
  *   Randall Jesup <rjesup@wgate.com>
@@ skipping 458 matching lines @@
     m_hadVerticalScrollbarBeforeRelayout = val;
   }
 
   StickyConstraintsMap& stickyConstraintsMap() {
     return ensureRareData().m_stickyConstraintsMap;
   }
   void invalidateAllStickyConstraints();
   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();
 
  private:
   explicit PaintLayerScrollableArea(PaintLayer&);
 
   bool hasHorizontalOverflow() const;
   bool hasVerticalOverflow() const;
   bool hasScrollableHorizontalOverflow() const;
@@ skipping 35 matching lines @@
   ScrollingCoordinator* getScrollingCoordinator() const;
 
   PaintLayerScrollableAreaRareData* rareData() { return m_rareData.get(); }
 
   PaintLayerScrollableAreaRareData& ensureRareData() {
     if (!m_rareData)
       m_rareData = WTF::makeUnique<PaintLayerScrollableAreaRareData>();
     return *m_rareData.get();
   }
 
+  bool layerNeedsCompositedScrolling(const LCDTextMode, const PaintLayer*);
   PaintLayer& m_layer;
 
   PaintLayer* m_nextTopmostScrollChild;
   PaintLayer* m_topmostScrollChild;
 
   // Keeps track of whether the layer is currently resizing, so events can cause
   // resizing to start and stop.
   unsigned m_inResizeMode : 1;
   unsigned m_scrollsOverflow : 1;
 
@@ skipping 31 matching lines @@
   // LayoutObject to hold our custom scroll corner.
   LayoutScrollbarPart* m_scrollCorner;
 
   // LayoutObject to hold our custom resizer.
   LayoutScrollbarPart* m_resizer;
 
   ScrollAnchor m_scrollAnchor;
 
   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
 };
 
 DEFINE_TYPE_CASTS(PaintLayerScrollableArea,
                   ScrollableArea,
                   scrollableArea,
                   scrollableArea->isPaintLayerScrollableArea(),
                   scrollableArea.isPaintLayerScrollableArea());
 
 }  // namespace blink
 
 #endif  // LayerScrollableArea_h