Handle nested position:sticky elements

cc/trees/property_tree.h

Index: cc/trees/property_tree.h
diff --git a/cc/trees/property_tree.h b/cc/trees/property_tree.h
index 58d4f5f823d3cdf8e1e8937f279dc7abac405666..0e2dfda382dd7de66915cdea0952f9c21fa4875e 100644
--- a/cc/trees/property_tree.h
+++ b/cc/trees/property_tree.h
@@ -114,7 +114,13 @@ struct StickyPositionNodeData {
   // by computing the additional offset necessary to keep the element stuck.
   gfx::Vector2dF main_thread_offset;
 
-  StickyPositionNodeData() : scroll_ancestor(-1) {}
+  int nearest_node_shifting_sticky_box;
+  int nearest_node_shifting_containing_block;
+
+  StickyPositionNodeData()
+      : scroll_ancestor(-1),
+        nearest_node_shifting_sticky_box(-1),
+        nearest_node_shifting_containing_block(-1) {}
 };
 
 class CC_EXPORT TransformTree final : public PropertyTree<TransformNode> {