Unify the calculation of main thread offset of sticky element

third_party/WebKit/Source/core/page/scrolling/StickyPositionScrollingConstraints.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef StickyPositionScrollingConstraints_h
 #define StickyPositionScrollingConstraints_h
 
 #include "platform/geometry/FloatRect.h"
 #include "platform/geometry/FloatSize.h"
 
 namespace blink {
 
 class LayoutBoxModelObject;
+class PaintLayer;
 
 class StickyPositionScrollingConstraints final {
  public:
   enum AnchorEdgeFlags {
     kAnchorEdgeLeft = 1 << 0,
     kAnchorEdgeRight = 1 << 1,
     kAnchorEdgeTop = 1 << 2,
     kAnchorEdgeBottom = 1 << 3
   };
   typedef unsigned AnchorEdges;
@@ skipping 25 matching lines @@
         total_sticky_box_sticky_offset_(other.total_sticky_box_sticky_offset_),
         total_containing_block_sticky_offset_(
             other.total_containing_block_sticky_offset_) {}
 
   FloatSize ComputeStickyOffset(
       const FloatRect& viewport_rect,
       const StickyPositionScrollingConstraints* ancestor_sticky_box_constraints,
       const StickyPositionScrollingConstraints*
           ancestor_containing_block_constraints);
 
+  FloatSize ComputeMainThreadStickyOffset(

[flackr, 2017/06/02 15:33:58]

Let's make this like GetTotalStickyBoxStickyOffset - i.e. maybe call it
GetLocalStickyOffset and move it amongst those functions.

[yigu, 2017/06/02 17:59:56]

Done.

+      const PaintLayer& ancestor_overflow_layer) const;
+
   bool HasAncestorStickyElement() const {
     return nearest_sticky_box_shifting_sticky_box_ ||
            nearest_sticky_box_shifting_containing_block_;
   }
 
   AnchorEdges GetAnchorEdges() const { return anchor_edges_; }
   bool HasAnchorEdge(AnchorEdgeFlags flag) const {
     return anchor_edges_ & flag;
   }
   void AddAnchorEdge(AnchorEdgeFlags edge_flag) { anchor_edges_ |= edge_flag; }
@@ skipping 108 matching lines @@
   // constraining block constriant rect for different sticky descendants is
   // quite complex. See the StickyPositionComplexTableNesting test in
   // LayoutBoxModelObjectTest.cpp.
   FloatSize total_sticky_box_sticky_offset_;
   FloatSize total_containing_block_sticky_offset_;
 };
 
 }  // namespace blink
 
 #endif  // StickyPositionScrollingConstraints_h