The PRESUBMIT code is basically a stripped-down copy of the code in
Chromium's src/PRESUBMIT.py.
BUG=chromium:498746
TESTED=I verified with 'git cl presubmit' that the existing
error was found. Then I ran it again after fixing it, with
presubmit passing.
NOTRY=True
Review URL: https://codereview.webrtc.org/1682393002
Cr-Commit-Position: refs/heads/master@{#11572}