This is outside of the DevTools component, one can use console API in Blink or content to report it.

meacer@, could you help re-triage this issue since you're the original reporter? Thanks!

I think two reasonable places to put this would be

1) DocumentLoader::DidCommitNavigation in blink (where the Legacy Symantec Cert console warning is)
2) c/b/ssl/SecurityStateTabHelper::DidFinishNavigation

I made a quick CL for (2) at https://crrev.com/c/837029 but haven't written any tests for it yet. I quickly found a soon-to-expire cert [1] via Censys [2], and checked that the console warning displays as desired.

No worries if we decide to not add this now, but I do think it would be a useful reminder to reduce unintentionally expired certificates.

[1] https://www.marekashley.com
[2] https://censys.io/certificates?q=parsed.validity.end%3A+2017-12-21

(Specifically, this takes the very simple route of generating a console warning message rather than adding a bullet to the security panel.)

Do we have any strong opinions about how far-out the warning should happen? 48 hours seems like a good base to go with if not.

After discussing with estark@ I changed the CL to display in the Security Panel instead. Since it's no longer potentially clogging the console output, would warning sooner be better?

Thanks for taking this Chris. I'd love to have a week of notice in advance, but perhaps that won't be effective as it's too far in the future. So 48 hours SGTM as a starting point.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/96fba2ff8246938a93a8da7e69b25103f3381762

commit 96fba2ff8246938a93a8da7e69b25103f3381762
Author: Christopher Thompson <cthomp@chromium.org>
Date: Tue Jan 09 17:13:15 2018

Add security panel bullet for expiring SSL certs

This adds a Security Panel info bullet for sites that have an SSL
certificate which is expiring in soon (<48 hours from now). This may
help some developers notice expiring certificates that they had
otherwise forgotten about.

Bug:  690711 
Change-Id: I7af4e2bd70bbadf73c93c4bb1e379df260d26414
Reviewed-on: https://chromium-review.googlesource.com/837029
Reviewed-by: Emily Stark <estark@chromium.org>
Reviewed-by: David Benjamin <davidben@chromium.org>
Commit-Queue: Christopher Thompson <cthomp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#528023}
[modify] https://crrev.com/96fba2ff8246938a93a8da7e69b25103f3381762/components/security_state/content/DEPS
[modify] https://crrev.com/96fba2ff8246938a93a8da7e69b25103f3381762/components/security_state/content/content_utils.cc
[modify] https://crrev.com/96fba2ff8246938a93a8da7e69b25103f3381762/components/security_state/content/content_utils_unittest.cc
[modify] https://crrev.com/96fba2ff8246938a93a8da7e69b25103f3381762/components/security_state_strings.grdp