After modifying testing/buildbot/filters/mojo.fyi.network_browser_tests.filter, the presubmit fails due to a Python error (FWIW, /usr/bin/python is version 3 (ArchLinux), but the "python" in PATH is Python 2).
For now I am now using "git cl upload --bypass-hooks" to bypass the error...

$ git cl upload
Running presubmit upload checks ...
Done processing (... cut ...)

** Presubmit ERRORS **
generate_buildbot_json_coveragetest (0.04s) failed
Traceback (most recent call last):
  File "generate_buildbot_json_coveragetest.py", line 35, in <module>
    sys.exit(main())
  File "generate_buildbot_json_coveragetest.py", line 19, in main
    cov = coverage.coverage(include='*generate_buildbot_json.py')
TypeError: __init__() got an unexpected keyword argument 'include'


Presubmit checks took 3.9s to calculate.

Was the presubmit check useful? If not, run "git cl presubmit -v"
to figure out which PRESUBMIT.py was run, then run git blame
on the file to figure out who to ask for help.



$ git cl presubmit -v
Running presubmit commit checks ...
Running /path/to/src/PRESUBMIT.py
Running /path/to/src/chrome/PRESUBMIT.py
Running /path/to/src/chrome/browser/PRESUBMIT.py
Running /path/to/src/chrome/browser/ui/webui/PRESUBMIT.py
Running /path/to/src/extensions/browser/PRESUBMIT.py
Running /path/to/src/testing/PRESUBMIT.py
[I2017-12-27 19:35:54,522 14238 140164486292672 presubmit_canned_checks.py] Skipping pylint: no matching changes.
Running /path/to/src/testing/buildbot/PRESUBMIT.py
Running /path/to/src/testing/buildbot/filters/PRESUBMIT.py

** Presubmit Messages **
generate_buildbot_json (0.21s)

generate_buildbot_json_unittest (0.03s)

manage (0.36s)

** Presubmit ERRORS **
Missing LGTM from an OWNER for these files:
    (... cut ...)

generate_buildbot_json_coveragetest (0.06s) failed
Traceback (most recent call last):
  File "generate_buildbot_json_coveragetest.py", line 35, in <module>
    sys.exit(main())
  File "generate_buildbot_json_coveragetest.py", line 19, in main
    cov = coverage.coverage(include='*generate_buildbot_json.py')
TypeError: __init__() got an unexpected keyword argument 'include'


Presubmit checks took 8.1s to calculate.