Compute and include the offset of the sticky box to its enclosing composited layer.

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 284 matching lines @@
     } else {
       sticky = layoutObject()->view()->frameView()->isScrollable();
     }
   }
 
   WebLayerStickyPositionConstraint webConstraint;
   if (sticky) {
     const StickyPositionScrollingConstraints& constraints =
         ancestorOverflowLayer->getScrollableArea()->stickyConstraintsMap().get(
             &m_owningLayer);
+
+    // Find the layout offset of the unshifted sticky box within its enclosing layer.
+    LayoutPoint enclosingLayerOffset;
+    m_owningLayer.enclosingLayerWithCompositedLayerMapping(ExcludeSelf)
+        ->convertToLayerCoords(m_owningLayer.ancestorOverflowLayer(),
+                               enclosingLayerOffset);
+    FloatPoint stickyBoxOffset =
+        constraints.scrollContainerRelativeStickyBoxRect().location();
+    stickyBoxOffset.moveBy(FloatPoint(-enclosingLayerOffset));
+
     webConstraint.isSticky = true;
     webConstraint.isAnchoredLeft =
         constraints.anchorEdges() &
         StickyPositionScrollingConstraints::AnchorEdgeLeft;
     webConstraint.isAnchoredRight =
         constraints.anchorEdges() &
         StickyPositionScrollingConstraints::AnchorEdgeRight;
     webConstraint.isAnchoredTop =
         constraints.anchorEdges() &
         StickyPositionScrollingConstraints::AnchorEdgeTop;
     webConstraint.isAnchoredBottom =
         constraints.anchorEdges() &
         StickyPositionScrollingConstraints::AnchorEdgeBottom;
     webConstraint.leftOffset = constraints.leftOffset();
     webConstraint.rightOffset = constraints.rightOffset();
     webConstraint.topOffset = constraints.topOffset();
     webConstraint.bottomOffset = constraints.bottomOffset();
+    webConstraint.parentRelativeStickyBoxOffset =
+        roundedIntPoint(stickyBoxOffset);
     webConstraint.scrollContainerRelativeStickyBoxRect =
         enclosingIntRect(constraints.scrollContainerRelativeStickyBoxRect());
     webConstraint.scrollContainerRelativeContainingBlockRect = enclosingIntRect(
         constraints.scrollContainerRelativeContainingBlockRect());
   }
 
   m_graphicsLayer->setStickyPositionConstraint(webConstraint);
 }
 
 void CompositedLayerMapping::updateLayerBlendMode(const ComputedStyle& style) {
@@ skipping 2821 matching lines @@
   } else if (graphicsLayer == m_scrollingContentsLayer.get()) {
     name = "Scrolling Contents Layer";
   } else {
     ASSERT_NOT_REACHED();
   }
 
   return name;
 }
 
 }  // namespace blink