Comment 37 for bug 1491566

My take on the backtrace is that the set_screen_power_mode request hangs somewhere in Mir, and since it holds the lock, it blocks both dimmer_alarm_notification and keep_display_on_temporarily (which is a result of user input). If my assumption is correct, we need to find why and where in Mir we block, so it would be great if we had debug symbols for mir (and libstdc++ and libc) for the USC backtrace.