In this run, it seems that the test failed for some reason, and then the test harness itself raised an exception:

https://logs.chromium.org/v/?s=chromium%2Fbb%2Ftryserver.chromium.win%2Fwin10_chromium_x64_rel_ng%2F106246%2F%2B%2Frecipes%2Fsteps%2Ftest_installer__with_patch_%2F0%2Fstdout

it's not clear to me what went wrong with the bring-up of a browser process, but here's the python exception details:

Traceback (most recent call last):
  File "test_chrome_with_chromedriver.py", line 117, in <module>
    sys.exit(main())
  File "test_chrome_with_chromedriver.py", line 106, in main
    with CreateChromedriver(args) as driver:
  File "C:\b\depot_tools\win_tools-2_7_6_bin\python\bin\lib\contextlib.py", line 17, in __enter__
    return self.gen.next()
  File "test_chrome_with_chromedriver.py", line 65, in CreateChromedriver
    driver.quit()
UnboundLocalError: local variable 'driver' referenced before assignment
ERROR