This methods returns the schema used by Granite.Widgets.Utils.get_default_close_button_position to determine the close button placement. It will first check for the pantheon/gala schema and then fallback to the default gnome one. If neither is available, null is returned. Make sure to check for this case, as otherwise your program may crash on startup.
the schema name. If the layout could not be determined, a warning will be thrown and null will be returned