cc : Move screen space scale factor to root transform node

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 10896439072f987cfb54ea841abca1122b156359..f2f481f81b8ecf689b40659da178014e3b7aa948 100644
--- a/cc/trees/property_tree.h
+++ b/cc/trees/property_tree.h
@@ -224,6 +224,10 @@ class CC_EXPORT TransformTree final : public PropertyTree<TransformNode> {
   void SetDeviceTransform(const gfx::Transform& transform,
                           gfx::PointF root_position);
   void SetDeviceTransformScaleFactor(const gfx::Transform& transform);
+  void SetScreenSpaceScale(float device_scale_factor,
+                           float page_scale_factor_for_root,
+                           gfx::Transform device_transform);
+
   float device_transform_scale_factor() const {
     return device_transform_scale_factor_;
   }