Unify the calculation of main thread offset of sticky element

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 49 matching lines @@
 
 class ComputedStyle;
 class HitTestResult;
 class LayoutBox;
 class LayoutScrollbarPart;
 class PaintLayer;
 class ScrollingCoordinator;
 class StickyPositionScrollingConstraints;
 class SubtreeLayoutScope;
 
-typedef WTF::HashMap<PaintLayer*, StickyPositionScrollingConstraints>
-    StickyConstraintsMap;
-
 struct CORE_EXPORT PaintLayerScrollableAreaRareData {
   WTF_MAKE_NONCOPYABLE(PaintLayerScrollableAreaRareData);
   USING_FAST_MALLOC(PaintLayerScrollableAreaRareData);
 
  public:
   PaintLayerScrollableAreaRareData();
 
   StickyConstraintsMap sticky_constraints_map_;
 };
 
@@ skipping 529 matching lines @@
 
 DEFINE_TYPE_CASTS(PaintLayerScrollableArea,
                   ScrollableArea,
                   scrollableArea,
                   scrollableArea->IsPaintLayerScrollableArea(),
                   scrollableArea.IsPaintLayerScrollableArea());
 
 }  // namespace blink
 
 #endif  // LayerScrollableArea_h