/usr/share/xsessions/gnome.desktop is in gnome-session 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 3 4 5 6 7 8 9 | [Desktop Entry]
Name=Ubuntu
Comment=This session logs you into Ubuntu
Exec=gnome-session --session=ubuntu
TryExec=gnome-session
Icon=
Type=Application
Hidden=true
X-Ubuntu-Gettext-Domain=gnome-session-3.0
|