cc: Construct the RSLL without using layer hierarchy

cc/trees/property_tree.h

 // Copyright 2014 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_TREES_PROPERTY_TREE_H_
 #define CC_TREES_PROPERTY_TREE_H_
 
 #include <stddef.h>
 
 #include <unordered_map>
@@ skipping 288 matching lines @@
   gfx::Size bounds;
   bool max_scroll_offset_affected_by_page_scale;
   bool is_inner_viewport_scroll_layer;
   bool is_outer_viewport_scroll_layer;
   gfx::Vector2dF offset_to_transform_parent;
   bool should_flatten;
   bool user_scrollable_horizontal;
   bool user_scrollable_vertical;
   int element_id;
   int transform_id;
+  // Number of drawn layers pointing to this node or any of its descendants.
+  int num_drawn_descendants;
 
   bool operator==(const ScrollNodeData& other) const;
 
   void ToProtobuf(proto::TreeNode* proto) const;
   void FromProtobuf(const proto::TreeNode& proto);
 };
 
 typedef TreeNode<ScrollNodeData> ScrollNode;
 
 class PropertyTrees;
@@ skipping 364 matching lines @@
 
  private:
   gfx::Vector2dF inner_viewport_container_bounds_delta_;
   gfx::Vector2dF outer_viewport_container_bounds_delta_;
   gfx::Vector2dF inner_viewport_scroll_bounds_delta_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_PROPERTY_TREE_H_