dbusService: Handle shell restarts better

Our D-Bus services don't make sense outside a GNOME session, so
they shut down automatically when gnome-shell is not on the bus.

However this does not only apply when activating a service from
a non-GNOME session, but also when restarting gnome-shell on Xorg.

This is particularly problematic for services that shut down
automatically, as they lose all tracking state, even when
re-activated.

Address this by queuing a shutdown check instead of shutting down
immediately, so that the service can pick up the new shell name
provided it appears before the timeout (i.e. two seconds).

Closes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/7843
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3463>

js/dbusServices/dbusService.js

@@ -30,6 +30,12 @@ export class ServiceImplementation {
             (c, name, owner) => (this._shellName = owner),
             () => {
                 this._shellName = null;
+
+                // For auto-shutdown services, delay shutting
+                // down in case the shell reappears
+                if (this._autoShutdown)
+                    this._queueShutdownCheck();
+                else
                     this.emit('shutdown');
             });
 
@@ -104,7 +110,7 @@ export class ServiceImplementation {
         if (GLib.getenv('SHELL_DBUS_PERSIST'))
             return;
 
-        if (this._holdCount > 0)
+        if (this._shellName && this._holdCount > 0)
             return;
 
         this.emit('shutdown');