[screenlocker] Start grace time when the greeter is shown
Review Request #124917 - Created Aug. 25, 2015 and submitted
So far the grace time started with the idle timeout. Given that our greeter takes a few seconds to start it rendered a short grace time useless as it was quite likely that the grace time already ended when the first visible feedback was shown to the user. Now the grace time starts when the greeter is actually shown.
- grace time of 5 sec: waited for the lock screen to show, counted to 4, moved mouse -> unlocked
- waited till the lock screen was shown and a few minutes more, moved mouse -> no unlock