cc: Construct the RSLL without using layer hierarchy

cc/trees/property_tree.cc

Index: cc/trees/property_tree.cc
diff --git a/cc/trees/property_tree.cc b/cc/trees/property_tree.cc
index 91dd5c73a27d758af37a5b9b3c838ae5cfe5aa7c..008cb7ef53b6a173934655e445fb0f89bec4a5f9 100644
--- a/cc/trees/property_tree.cc
+++ b/cc/trees/property_tree.cc
@@ -528,7 +528,8 @@ ScrollNodeData::ScrollNodeData()
       user_scrollable_horizontal(false),
       user_scrollable_vertical(false),
       element_id(0),
-      transform_id(0) {}
+      transform_id(0),
+      num_drawn_descendants(0) {}
 
 ScrollNodeData::ScrollNodeData(const ScrollNodeData& other) = default;