Move logic of recording main thread scrolling reasons from cc to blink::ScrollManager

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 461 matching lines @@
   bool HadVerticalScrollbarBeforeRelayout() const {
     return had_vertical_scrollbar_before_relayout_;
   }
   void SetHadVerticalScrollbarBeforeRelayout(bool val) {
     had_vertical_scrollbar_before_relayout_ = val;
   }
 
   StickyConstraintsMap& GetStickyConstraintsMap() {
     return EnsureRareData().sticky_constraints_map_;
   }
+
   void InvalidateAllStickyConstraints();
   void InvalidateStickyConstraintsFor(PaintLayer*,
                                       bool needs_compositing_update = true);
-
-  void RemoveStyleRelatedMainThreadScrollingReasons();
-  void AddStyleRelatedMainThreadScrollingReasons(const uint32_t);
-  bool HasMainThreadScrollingReason(uint32_t reason) const {
-    return reasons_ & reason;
+  uint32_t GetNonCompositedMainThreadScrollingReasons() {
+    return non_composited_main_thread_scrolling_reasons_;
   }
 
   uint64_t Id() const;
 
   DECLARE_VIRTUAL_TRACE();
 
  private:
   explicit PaintLayerScrollableArea(PaintLayer&);
 
   bool HasHorizontalOverflow() const;
@@ skipping 90 matching lines @@
   LayoutScrollbarPart* scroll_corner_;
 
   // LayoutObject to hold our custom resizer.
   LayoutScrollbarPart* resizer_;
 
   ScrollAnchor scroll_anchor_;
 
   std::unique_ptr<PaintLayerScrollableAreaRareData> rare_data_;
 
   // MainThreadScrollingReason due to the properties of the LayoutObject
-  uint32_t reasons_;
+  uint32_t non_composited_main_thread_scrolling_reasons_;

[tdresser, 2017/04/11 18:50:47]

Is "non composited" redundant with "main thread"?

[yigu, 2017/04/11 21:28:11]

This is to differentiate the reasons that caused main thread scrolling for an
element but we also "composite" that element. e.g. element with fixed background
attachment and "will-change:transform;".

 
 #if DCHECK_IS_ON()
   bool has_been_disposed_;
 #endif
 };
 
 DEFINE_TYPE_CASTS(PaintLayerScrollableArea,
                   ScrollableArea,
                   scrollableArea,
                   scrollableArea->IsPaintLayerScrollableArea(),
                   scrollableArea.IsPaintLayerScrollableArea());
 
 }  // namespace blink
 
 #endif  // LayerScrollableArea_h