cc : Move screen space scale factor to root transform node

cc/trees/property_tree_builder.cc

Index: cc/trees/property_tree_builder.cc
diff --git a/cc/trees/property_tree_builder.cc b/cc/trees/property_tree_builder.cc
index edc102623e0f4d50260d61e4b7850fde76c12804..0c95c45e0bad551335ab4867ff14692cacbdb40a 100644
--- a/cc/trees/property_tree_builder.cc
+++ b/cc/trees/property_tree_builder.cc
@@ -630,12 +630,10 @@ bool AddTransformNodeIfNeeded(
   }
 
   float post_local_scale_factor = 1.0f;
-  if (is_root)
-    post_local_scale_factor =
-        data_for_children->property_trees->transform_tree.device_scale_factor();
 
   if (is_page_scale_layer) {
-    post_local_scale_factor *= data_from_ancestor.page_scale_factor;
+    if (!is_root)
+      post_local_scale_factor *= data_from_ancestor.page_scale_factor;
     data_for_children->property_trees->transform_tree.set_page_scale_factor(
         data_from_ancestor.page_scale_factor);
   }
@@ -1339,6 +1337,10 @@ void BuildPropertyTreesTopLevelInternal(
     draw_property_utils::UpdateElasticOverscroll(
         property_trees, overscroll_elasticity_layer, elastic_overscroll);
     property_trees->clip_tree.SetViewportClip(gfx::RectF(viewport));
+    float page_scale_factor_for_root =
+        page_scale_layer == root_layer ? page_scale_factor : 1.f;
+    property_trees->transform_tree.SetScreenSpaceScale(
+        device_scale_factor, page_scale_factor_for_root, device_transform);
     property_trees->transform_tree.SetDeviceTransform(device_transform,
                                                       root_layer->position());
     return;
@@ -1379,11 +1381,17 @@ void BuildPropertyTreesTopLevelInternal(
       device_scale_factor);
   data_for_recursion.safe_opaque_background_color = color;
 
+  float page_scale_factor_for_root =
+      page_scale_layer == root_layer ? page_scale_factor : 1.f;
+  data_for_recursion.property_trees->transform_tree.SetScreenSpaceScale(
+      device_scale_factor, page_scale_factor_for_root, device_transform);
+
   ClipNode root_clip;
   root_clip.resets_clip = true;
   root_clip.applies_local_clip = true;
   root_clip.clip = gfx::RectF(viewport);
   root_clip.transform_id = kRootPropertyTreeNodeId;
+  root_clip.target_transform_id = kRootPropertyTreeNodeId;
   data_for_recursion.clip_tree_parent =
       data_for_recursion.property_trees->clip_tree.Insert(
           root_clip, kRootPropertyTreeNodeId);