Handle nested position:sticky elements

cc/layers/layer_sticky_position_constraint.h

Index: cc/layers/layer_sticky_position_constraint.h
diff --git a/cc/layers/layer_sticky_position_constraint.h b/cc/layers/layer_sticky_position_constraint.h
index 3f43bc7751ab614b2c12b25c18d73a71cd308012..71f40343c70d7b6864396937cef93d1c59bc2488 100644
--- a/cc/layers/layer_sticky_position_constraint.h
+++ b/cc/layers/layer_sticky_position_constraint.h
@@ -11,6 +11,8 @@
 
 namespace cc {
 
+class Layer;
+
 struct CC_EXPORT LayerStickyPositionConstraint {
   LayerStickyPositionConstraint();
   LayerStickyPositionConstraint(const LayerStickyPositionConstraint& other);
@@ -44,6 +46,14 @@ struct CC_EXPORT LayerStickyPositionConstraint {
   // 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;
 };