desktopui_ScreenLocker telemetry test should listen to DBUS ScreenLocked event.

BUG=chromium:338740
TEST=manual

Change-Id: I2018494d3813c29263cc05ce16a959de2991bac0
Reviewed-on: https://chromium-review.googlesource.com/203550
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Tested-by: Alexander Alekseev <alemate@chromium.org>
Reviewed-by: Chris Masone <cmasone@chromium.org>
Commit-Queue: Alexander Alekseev <alemate@chromium.org>
2 files changed