It looks like some Tast ARC tests aren't exiting when their deadlines are reached, which makes it a bit harder to debug failures (since you get a generic "Test timed out" error instead of descriptions of what they were waiting for).

arc.Boot at http://stainless/browse/chromeos-autotest-results/213673330-chromeos-test/
2018/07/02 16:00:24 [16:00:24.016] Waiting for Android boot
2018/07/02 16:02:02 [16:02:01.800] Error at bundle.go:210: Test timed out

arc.IntentForward at http://stainless/browse/chromeos-autotest-results/213673395-chromeos-test/
2018/07/02 16:19:53 [16:19:53.110] Waiting for Android boot
2018/07/02 16:21:35 [16:21:34.926] Error at bundle.go:210: Test timed out

I suspect that the problem is in waitProp in arc/boot_phase.go, which looks like it needs to check ctx.Err() -- if I'm not misreading, right now it loops forever and only returns on success.