Looks like it kicked in at least once here. From the feedback report (this is just the first hang I saw):

2017-12-04T10:56:54.008933-08:00 WARNING session_manager[1492]: [WARNING:liveness_checker_impl.cc(64)] Browser hang detected!
2017-12-04T10:56:54.008952-08:00 WARNING session_manager[1492]: [WARNING:liveness_checker_impl.cc(68)] Aborting browser process.
2017-12-04T10:56:54.009081-08:00 INFO session_manager[1492]: [INFO:browser_job.cc(164)] Terminating process: Browser did not respond to DBus liveness check.
2017-12-04T10:56:54.009099-08:00 INFO session_manager[1492]: [INFO:system_utils_impl.cc(93)] Sending 6 to 1529 as 1000
2017-12-04T10:56:54.239791-08:00 WARNING crash_reporter[4409]: Received crash notification for chrome[1529] user 1000 (called directly)
2017-12-04T10:56:57.009504-08:00 WARNING session_manager[1492]: [WARNING:browser_job.cc(172)] Aborting child process 1529's process group 3 seconds after sending signal
2017-12-04T10:56:57.009527-08:00 INFO session_manager[1492]: [INFO:browser_job.cc(156)] Terminating process group: Browser took more than 3 seconds to exit after signal.
2017-12-04T10:56:57.009535-08:00 INFO session_manager[1492]: [INFO:system_utils_impl.cc(93)] Sending 6 to -1529 as 1000
2017-12-04T10:56:57.047089-08:00 WARNING crash_reporter[4416]: [user] Received crash notification for chrome[1632] sig 6, user 1000 (ignoring call by kernel - chrome crash; waiting for chrome to call us directly)
2017-12-04T10:56:57.047090-08:00 WARNING crash_reporter[4415]: [user] Received crash notification for chrome[1224] sig 6, user 1000 (ignoring call by kernel - chrome crash; waiting for chrome to call us directly)
2017-12-04T10:56:57.047271-08:00 WARNING crash_reporter[4416]: [ARC] Received crash notification for chrome[1632] sig 6, user 1000 (ignoring - crash origin is not ARC)
2017-12-04T10:56:57.047280-08:00 WARNING crash_reporter[4415]: [ARC] Received crash notification for chrome[1224] sig 6, user 1000 (ignoring - crash origin is not ARC)
2017-12-04T10:56:57.640269-08:00 ERR session_manager[4442]: [ERROR:process.cc(329)] Exec of /usr/bin/vm_launcher fail<IPv6: 1> No such file or directory
2017-12-04T10:56:57.657751-08:00 WARNING crash_reporter[4444]: [user] Received crash notification for chrome[1529] sig 6, user 1000 (ignoring call by kernel - chrome crash; waiting for chrome to call us directly)
2017-12-04T10:56:57.658018-08:00 WARNING crash_reporter[4444]: [ARC] Received crash notification for chrome[1529] sig 6, user 1000 (ignoring - crash origin is not ARC)
2017-12-04T10:56:58.020928-08:00 ERR session_manager[4449]: [ERROR:process.cc(329)] Exec of /usr/bin/vm_launcher fail<IPv6: 1> No such file or directory
2017-12-04T10:56:58.145443-08:00 INFO session_manager[1492]: [INFO:child_exit_handler.cc(77)] Handling 1529 exit.
2017-12-04T10:56:58.145468-08:00 ERR session_manager[1492]: [ERROR:child_exit_handler.cc(85)]   Exited with signal 6
2017-12-04T10:56:58.145506-08:00 INFO session_manager[1492]: [INFO:session_manager_service.cc(289)] Exiting process is chrome.
2017-12-04T10:56:58.145523-08:00 INFO session_manager[1492]: [INFO:browser_job.cc(156)] Terminating process group: Ensuring browser processes are gone.

Here are the Chrome crashes from that client on Dec 4:

crash/b1b5e8dc1de5fb9f (SIGABRT, no symbols)
crash/4663adeaf1b6e357 (SIGABRT, bluetooth code)
crash/94a1ae3a2e7ff36b (SIGABRT, bluetooth code)
crash/5d98641a7e7b0bb1 (SIGABRT, no symbols)
crash/67ceadf5a28799e3 (SIGABRT, no symbols)

I think that the BT crashes' timestamps line up with the hang from the log, so I'd recommend starting there.

Mind filing a separate bug for proposed changes to the hang detection code so we're not talking about both that and this specific hang in the same place?

BT part is covered in issue 787167

I'm going to close this one and open a second issue to track changes to hang detection

I've documented the hang detection code at https://chromium.googlesource.com/chromiumos/platform2/+/master/login_manager/docs/chrome_hang_detection.md, so feel free to add a link to that in the other bug to help whoever's working on it.

Filed  bug 793880