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

third_party/WebKit/public/platform/WebLayerStickyPositionConstraint.h

Index: third_party/WebKit/public/platform/WebLayerStickyPositionConstraint.h
diff --git a/third_party/WebKit/public/platform/WebLayerStickyPositionConstraint.h b/third_party/WebKit/public/platform/WebLayerStickyPositionConstraint.h
index 83d04c64abf48b420d6152198f029fc40983c4b4..296496d76f24a22d2545fa38c5d5c6555e31f2ef 100644
--- a/third_party/WebKit/public/platform/WebLayerStickyPositionConstraint.h
+++ b/third_party/WebKit/public/platform/WebLayerStickyPositionConstraint.h
@@ -26,6 +26,9 @@
 #ifndef WebLayerStickyPositionConstraint_h
 #define WebLayerStickyPositionConstraint_h
 
+#include "public/platform/WebPoint.h"
+#include "public/platform/WebRect.h"
+
 namespace blink {
 
 // TODO(flackr): Combine with WebLayerPositionConstraint.
@@ -47,6 +50,10 @@ struct WebLayerStickyPositionConstraint {
   float topOffset;
   float bottomOffset;
 
+  // This is the layout position of the sticky element before it has been
+  // shifted relative to the enclosing composited layer.
+  WebPoint parentRelativeStickyBoxOffset;
+
   // The layout rectangle of the sticky element before it has been shifted
   // to stick.
   WebRect scrollContainerRelativeStickyBoxRect;