Unify the calculation of main thread offset of sticky element

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 796ab90f90a5e552b1d57ac53761dd70749e492b..798083a41a52e1e53dad1eaf3f777e9a77bb163a 100644
--- a/third_party/WebKit/public/platform/WebLayerStickyPositionConstraint.h
+++ b/third_party/WebKit/public/platform/WebLayerStickyPositionConstraint.h
@@ -51,10 +51,6 @@ struct WebLayerStickyPositionConstraint {
   float top_offset;
   float bottom_offset;
 
-  // This is the layout position of the sticky element before it has been
-  // shifted relative to the enclosing composited layer.
-  WebPoint parent_relative_sticky_box_offset;
-
   // The layout rectangle of the sticky element before it has been shifted
   // to stick.
   WebRect scroll_container_relative_sticky_box_rect;