It looks like Chrome is segfaulting. No symbols in the dumps, unfortunately.

This is still happening; see e.g. http://uberchromegw/i/chromeos.chrome/builders/tricky-tot-chrome-pfq-informational/builds/6349.

I'm having a hard time getting anything from the logs here. https://pantheon.corp.google.com/storage/browser/chromeos-image-archive/tricky-tot-chrome-pfq-informational/R63-10019.0.0-b6349/vm_test_results_2/pfq_suite/test_harness/all/SimpleTestUpdateAndVerify/2_autotest_tests/results-17-desktopui_ScreenLocker shows a timestamp of 10/10 11:02 for all of its files, but one of those files, "status", shows the test as failing at 12:39:13. The logs appear to stop before the test failure (maybe due to running out of disk space):

2017-10-10T17:27:03.366358+00:00 first boot (GMT)
2017-10-10T17:30:29.141018+00:00 shutdown for reboot
2017-10-10T10:30:32.871602-07:00 second boot (now PDT)
2017-10-10T10:38:34.470359-07:00 end (but disk is maybe full at this point) 

This looks like it might be caused by the GPU crash tracked in issue 772568. I'm still having trouble getting symbols, but minidump_dump indicates that chrome.20171010.123910.28969.dmp (just before the failure in #2) is from the GPU process.