From those 3 builders, Chrome range 481626 - 481653.

I will attempt to reproduce and bisect locally using Simple Chrome...

Failure output:

06/22 17:54:04.540 INFO | test_runner_utils:0199| autoserv| START	----	----	timestamp=1498172044	localtime=Jun 22 17:54:04
06/22 17:54:04.559 INFO | test_runner_utils:0199| autoserv| AUTOTEST_STATUS::	START	login_RetrieveActiveSessions	login_RetrieveActiveSessions	timestamp=1498172044	localtime=Jun 22 17:54:04
06/22 17:54:04.559 INFO | test_runner_utils:0199| autoserv| START	login_RetrieveActiveSessions	login_RetrieveActiveSessions	timestamp=1498172044	localtime=Jun 22 17:54:04
06/22 17:54:04.583 INFO | test_runner_utils:0199| autoserv| AUTOTEST_FETCH_PACKAGE:test-login_RetrieveActiveSessions.tar.bz2:/usr/local/autotest/packages/test-login_RetrieveActiveSessions.tar.bz2:/usr/local/autotest/tmp/_autotmp_Z25gdBharness-fifo/autoserv.fifo
06/22 17:54:04.583 INFO | test_runner_utils:0199| autoserv| send_file. source: /build/tricky/usr/local/build/autotest/packages/test-login_RetrieveActiveSessions.tar.bz2, dest: /usr/local/autotest/packages/test-login_RetrieveActiveSessions.tar.bz2, delete_dest: False,preserve_symlinks:False
06/22 17:54:04.583 INFO | test_runner_utils:0199| autoserv| Using Rsync.
06/22 17:54:04.583 INFO | test_runner_utils:0199| autoserv| Running 'rsync -L  --timeout=1800 --rsh='/usr/bin/ssh -a -x  -F /dev/null -i /dev/null -o ControlPath=/tmp/_autotmp_1r7ZbHssh-master/socket -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -o BatchMode=yes -o ConnectTimeout=30 -o ServerAliveInterval=900 -o ServerAliveCountMax=3 -o ConnectionAttempts=4 -o Protocol=2 -l root -p 9228' -az --no-o --no-g "/build/tricky/usr/local/build/autotest/packages/test-login_RetrieveActiveSessions.tar.bz2" "root@127.0.0.1:"/usr/local/autotest/packages/test-login_RetrieveActiveSessions.tar.bz2""'
06/22 17:54:04.609 INFO | test_runner_utils:0199| autoserv| /build/tricky/usr/local/build/autotest/server/hosts/ssh_host.py:295: UserWarning: Caller to run_very_slowly() is <module>|main|run_autoserv|run|run|_execute_code|<module>|parallel_simple|parallel_simple|run_client|run|_do_run|execute_control|execute_section|_execute_daemon|run|wrapper|run_very_slowly|_run|run|join_bg_jobs|_wait_for_commands|process_output|write|_process_line|_process_line|run|wrapper|run_very_slowly|_get_server_stack_state
06/22 17:54:04.609 INFO | test_runner_utils:0199| autoserv| warnings.warn("Caller to run_very_slowly() is %s" % stack)
06/22 17:54:04.609 INFO | test_runner_utils:0199| autoserv| 
06/22 17:54:04.609 INFO | test_runner_utils:0199| autoserv| Running (ssh) 'echo B > /usr/local/autotest/tmp/_autotmp_Z25gdBharness-fifo/autoserv.fifo'
06/22 17:54:04.636 INFO | test_runner_utils:0199| autoserv| AUTOTEST_FETCH_PACKAGE:packages.checksum:/usr/local/autotest/packages.checksum:/usr/local/autotest/tmp/_autotmp_bFXIkEharness-fifo/autoserv.fifo
06/22 17:54:04.636 INFO | test_runner_utils:0199| autoserv| send_file. source: /build/tricky/usr/local/build/autotest/packages/packages.checksum, dest: /usr/local/autotest/packages.checksum, delete_dest: False,preserve_symlinks:False
06/22 17:54:04.636 INFO | test_runner_utils:0199| autoserv| Using Rsync.
06/22 17:54:04.637 INFO | test_runner_utils:0199| autoserv| Running 'rsync -L  --timeout=1800 --rsh='/usr/bin/ssh -a -x  -F /dev/null -i /dev/null -o ControlPath=/tmp/_autotmp_1r7ZbHssh-master/socket -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -o BatchMode=yes -o ConnectTimeout=30 -o ServerAliveInterval=900 -o ServerAliveCountMax=3 -o ConnectionAttempts=4 -o Protocol=2 -l root -p 9228' -az --no-o --no-g "/build/tricky/usr/local/build/autotest/packages/packages.checksum" "root@127.0.0.1:"/usr/local/autotest/packages.checksum""'
06/22 17:54:04.662 INFO | test_runner_utils:0199| autoserv| /build/tricky/usr/local/build/autotest/server/hosts/ssh_host.py:295: UserWarning: Caller to run_very_slowly() is <module>|main|run_autoserv|run|run|_execute_code|<module>|parallel_simple|parallel_simple|run_client|run|_do_run|execute_control|execute_section|_execute_daemon|run|wrapper|run_very_slowly|_run|run|join_bg_jobs|_wait_for_commands|process_output|write|_process_line|run|wrapper|run_very_slowly|_get_server_stack_state
06/22 17:54:04.662 INFO | test_runner_utils:0199| autoserv| warnings.warn("Caller to run_very_slowly() is %s" % stack)
06/22 17:54:04.662 INFO | test_runner_utils:0199| autoserv| 
06/22 17:54:04.662 INFO | test_runner_utils:0199| autoserv| Running (ssh) 'echo B > /usr/local/autotest/tmp/_autotmp_bFXIkEharness-fifo/autoserv.fifo'
06/22 17:54:07.122 INFO | test_runner_utils:0199| autoserv| AUTOTEST_STATUS::		ERROR	login_RetrieveActiveSessions	login_RetrieveActiveSessions	timestamp=1498172046	localtime=Jun 22 17:54:06	Could not stop session
06/22 17:54:07.123 INFO | test_runner_utils:0199| autoserv| ERROR	login_RetrieveActiveSessions	login_RetrieveActiveSessions	timestamp=1498172046	localtime=Jun 22 17:54:06	Could not stop session
06/22 17:54:07.127 INFO | test_runner_utils:0199| autoserv| AUTOTEST_STATUS::	END ERROR	login_RetrieveActiveSessions	login_RetrieveActiveSessions	timestamp=1498172046	localtime=Jun 22 17:54:06
06/22 17:54:07.127 INFO | test_runner_utils:0199| autoserv| END ERROR	login_RetrieveActiveSessions	login_RetrieveActiveSessions	timestamp=1498172046	localtime=Jun 22 17:54:06

login screen looks broken on ToT (user pod is at the right, bottom corner).
I wonder if it's related. +xiyuan@

OK, I have been able to repro this locally, and confirmed that @481626 is good and @481653 is bad.

My first guess @481630 is still good, so bisecting from 481630-481653.

Tracked this down to master@{#481640}: https://chromium-review.googlesource.com/540536

This has already been reverted and triaged in issue 736251