Handle nested position:sticky elements

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"
 
 namespace cc {
 
+class Layer;
+
 struct CC_EXPORT LayerStickyPositionConstraint {
   LayerStickyPositionConstraint();
   LayerStickyPositionConstraint(const LayerStickyPositionConstraint& other);
 
   bool is_sticky : 1;
   bool is_anchored_left : 1;
   bool is_anchored_right : 1;
   bool is_anchored_top : 1;
   bool is_anchored_bottom : 1;
 
@@ skipping 13 matching lines @@
   // 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;
 
+  Layer* nearest_layer_shifting_sticky_box;
+  Layer* nearest_layer_shifting_containing_block;
+
+  gfx::Vector2dF total_sticky_box_sticky_offset;
+  gfx::Vector2dF total_containing_block_sticky_offset;

[flackr, 2017/02/21 00:32:43]

These only need to be in the StickyPositionNodeData right? Since we update and
use these during the transform tree update.

+
+  gfx::Vector2dF cached_computed_sticky_offset;
+
   bool operator==(const LayerStickyPositionConstraint&) const;
   bool operator!=(const LayerStickyPositionConstraint&) const;
 };
 
 }  // namespace cc
 
 #endif  // CC_LAYERS_LAYER_STICKY_POSITION_CONSTRAINT_H_