Comment 25 for bug 528094

Just looked at the code a little, though I'm not really familiar with the internal Gnome architecture at all. It looks like indicator-session is where things go down. session_service.c is where the Lock Screen item is actually provided for the menu, and lock-helper.c (function lock_screen()) is where it actually is making the call. It's making a dbus call, but again, as I really don't know anything about dbus, my ability to trace further ends without some actual knowledge / work on my part. :)