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 6edac892bc4636e2022d51fb1fd4d79f137ae9bc..ee5b86d81c19d6969ba5f6ea446a9935eaf52941 100644
--- a/cc/trees/property_tree.h
+++ b/cc/trees/property_tree.h
@@ -227,6 +227,10 @@ 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_;
   }