The arc.Boot Tast test started failing recently:

2018/08/17 23:35:30 Started test arc.Boot
2018/08/17 23:35:30 [23:35:29.532] Restarting ui job
2018/08/17 23:35:31 [23:35:30.952] Waiting for org.chromium.SessionManager D-Bus service
2018/08/17 23:35:31 [23:35:30.953] Asking session_manager to enable Chrome testing
2018/08/17 23:35:31 [23:35:30.953] Waiting for Chrome to write its debugging port to /home/chronos/DevToolsActivePort
2018/08/17 23:35:32 [23:35:31.451] Removing cryptohome for testuser@gmail.com
2018/08/17 23:35:32 [23:35:31.470] Finding OOBE DevTools target
2018/08/17 23:35:32 [23:35:31.553] Connecting to Chrome at ws://127.0.0.1:32834/devtools/page/1D34195E6A9A1A372F3330A4DA16EF23
2018/08/17 23:35:32 [23:35:31.604] Waiting for OOBE
2018/08/17 23:35:33 [23:35:32.954] Logging in as user "testuser@gmail.com"
2018/08/17 23:35:33 [23:35:33.015] Waiting for cryptohome /home/user/1b2a7d336acd41313d61cc2dec19f31446a5c681
2018/08/17 23:35:35 [23:35:35.058] Waiting for OOBE to be dismissed
2018/08/17 23:35:43 [23:35:42.630] Waiting for Android boot
2018/08/17 23:37:13 [23:37:12.628] Error at boot.go:39: Failed to start ARC: failed waiting org.chromium.arc.boot=1 (system_server crashed before BOOT_COMPLETED?): context deadline exceeded

http://stainless/search?view=matrix&row=builder_name&col=build&first_date=2018-08-12&last_date=2018-08-18&test=%5Etast%5C.arc%5C.Boot%24&exclude_cts=true&exclude_not_run=true&exclude_non_release=true&exclude_au=true&exclude_acts=true&exclude_retried=true&exclude_non_production=false

I think that http://ag/4736129 recently renamed org.chromium.arc.boot to ro.arc.boot_completed. The test passes locally for me when I rename it to match.