Unify the calculation of main thread offset of sticky element

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

Index: third_party/WebKit/Source/core/page/scrolling/StickyPositionScrollingConstraints.h
diff --git a/third_party/WebKit/Source/core/page/scrolling/StickyPositionScrollingConstraints.h b/third_party/WebKit/Source/core/page/scrolling/StickyPositionScrollingConstraints.h
index 330d2d86334c79ac8050a50cc8565bc97c06bfeb..36dfa4fffebb7065e77663884675f079859b55f5 100644
--- a/third_party/WebKit/Source/core/page/scrolling/StickyPositionScrollingConstraints.h
+++ b/third_party/WebKit/Source/core/page/scrolling/StickyPositionScrollingConstraints.h
@@ -11,6 +11,7 @@
 namespace blink {
 
 class LayoutBoxModelObject;
+class PaintLayer;
 
 class StickyPositionScrollingConstraints final {
  public:
@@ -56,6 +57,9 @@ class StickyPositionScrollingConstraints final {
       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_;