To do this, we now wait for the start/stop job to complete. We also have
two targets in gnome-session to ensure that everything is working as
expected.
In order to start the services, we simply request the
gnome-session-x11-services-ready.target unit, and wait for it to become
available. To stop, we use the gnome-session-x11-services.target unit
which should stop all services in a way that is entirely race free.
This requires both gnome-session and gnome-settings-daemon changes to
work (which are in the corresponding merge requests).
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/895
01a927f388