This isn't issue 5291, this has to do with using chromium's custom command line tool to edit commit messages, not PolyGerrit.

Moving to chromium project, as there are actually two issues on their end.

The first issue is I don't think git cl description signals its intent to suppress notification to Gerrit. Should it support the --send_mail flag in the same way as git cl upload? If no preference is given, should it obey Gerrit's WIP semantics (notifies unless WIP), or default to no email?

The second issue is that the code that git_cl.py depends on to edit the commit message no longer supports the notify argument. Its usage was inadvertently omitted here:

https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/544118

Moved issue gerrit:7055 to now be  issue chromium:757617 .

Thanks for raising this bug; looks like it was an oversight as Logan pointed out in his comment. Fix here: https://chromium-review.googlesource.com/634245

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/tools/depot_tools/+/5a4ef4537e27a403bcd583fb80870c16a12e1076

commit 5a4ef4537e27a403bcd583fb80870c16a12e1076
Author: Aaron Gable <agable@chromium.org>
Date: Wed Sep 06 00:08:25 2017

Don't send email from git-cl-description

The 'notify' parameter was accidentally left out in
https://crrev.com/c/544118. The calling code in git_cl.py
already sets notify='NONE', so this will suppress all
notifications as before.

Bug:  757617 
Change-Id: Ib0144d644d54b194fac0c0eb2fb51a6affa3340e
Reviewed-on: https://chromium-review.googlesource.com/634245
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>

[modify] https://crrev.com/5a4ef4537e27a403bcd583fb80870c16a12e1076/gerrit_util.py