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

cc/layers/layer_sticky_position_constraint.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_LAYERS_LAYER_STICKY_POSITION_CONSTRAINT_H_
 #define CC_LAYERS_LAYER_STICKY_POSITION_CONSTRAINT_H_
 
 #include "cc/base/cc_export.h"
 
 #include "ui/gfx/geometry/rect.h"
@@ skipping 14 matching lines @@
   bool is_anchored_top : 1;
   bool is_anchored_bottom : 1;
 
   // The offset from each edge of the ancestor scroller (or the viewport) to
   // try to maintain to the sticky box as we scroll.
   float left_offset;
   float right_offset;
   float top_offset;
   float bottom_offset;
 
+  // The layout offset of the sticky box relative to its containing layer.
+  // This is used to detect the sticky offset the main thread has applied
+  // to the layer.
+  gfx::Point parent_relative_sticky_box_offset;
+
   // The rectangle corresponding to original layout position of the sticky box
   // relative to the scroll ancestor. The sticky box is only offset once the
   // scroll has passed its initial position (e.g. top_offset will only push
   // the element down from its original position).
   gfx::Rect scroll_container_relative_sticky_box_rect;
 
   // The layout rectangle of the sticky box's containing block relative to the
   // scroll ancestor. The sticky box is only moved as far as its containing
   // block boundary.
   gfx::Rect scroll_container_relative_containing_block_rect;
 
   void ToProtobuf(proto::LayerStickyPositionConstraint* proto) const;
   void FromProtobuf(const proto::LayerStickyPositionConstraint& proto);
 
   bool operator==(const LayerStickyPositionConstraint&) const;
   bool operator!=(const LayerStickyPositionConstraint&) const;
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_STICKY_POSITION_CONSTRAINT_H_