/usr/share/glib-2.0/schemas/10_gnome-session-common.gschema.override is in gnome-session-common 3.2.1-0ubuntu8.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | [org.gnome.desktop.session]
session-name="ubuntu"
|