@extromium -- Thank you for the report.
Able to reproduce the issue on Latest Dev# 58.0.3004.3 on Windows, Mac and Linux.
This is a regression issue broken in M58. Below are the bisect details,
Chrome Good Build -- 57.0.2987.40 (Revision: 444943)
Chrome Bad Build  -- 58.0.2988.0  (Revision: 445272)
You are probably looking for a change made after 444955 (known good), but no later than 444956 (first known bad).
CHANGELOG URL:
  https://chromium.googlesource.com/chromium/src/+log/8127a839bf18e618aaf7a8cad95440c6cd3f9f76..464e47a82e253d08a7c7236fcf5cb5ec5bf8660b

Review URL -- https://codereview.chromium.org/2588643004

Adding the related Dev in Cc.

@ecobos -- Could you please look into the issue, kindly re-assign if this is not related to your changes.
Adding RB label as this is a recent Regression.
Thank You.

This was intentional as the acid3 test no longer matches the spec. Making sure the acid3 test is fixed was noted in the replies to the intent to ship. Emilio, did you report to acid3feedback@webstandards.org?

That address bounces my mail back, so I followed up on an existing www-style thread instead. Will post a link when it reaches the archives.

Well, the archive seems to have eaten my mail. Anyway, here it is the sent mail. 

I'll resend it if I don't get reply in a few days I guess.

Date: Thu, 9 Feb 2017 14:50:11 +0100
From: Emilio Cobos Álvarez <ecobos@igalia.com>
To: www-style@w3.org, ian@hixie.ch
Cc: ms2ger@gmail.com, acid3feedback@webstandards.org
Subject: Re: Acid3 and :first-child
Reply-To: CAP2znoberFeuey0U-KcMH+gtJXYJAPTL9wXkD9ygoj=o2DGyEQ@mail.gmail.com

Hi,

I would like to ask to get the test fixed too.

Blink has implemented this behavior now, and it's clear that the test
doesn't test any standard specification.

For discussion about whether the spec change is right or wrong, please
see this csswg-drafts issue[1] and the blink-dev thread[2].

Ian, any chance you would reconsider fixing this test?

 -- Emilio

[1]: https://github.com/w3c/csswg-drafts/issues/695
[2]: https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/RgdSWmv0s4g

Just to update the latest bahaviour :
still observed the issue on latest Canary#58.0.3012.0 on Windows 7,Mac 10.12.2 & Linux Ubuntu 14.04.
ecobos@Could you please look into this issue & update the thread.
Thank you.

I never received that mail to www-style, and I could not find it in the lists archive.

I bet it got filtered because of the bogus Reply-To header (which should've been In-Reply-To). Anyway, just re-sent it, and Cc'd you.

ecobos@/rune@: Removing the blocker label as per C#2 as this is intentional as per the spec. Please revert if this should still be blocking.

Thank you!

Friendly ping!!
ecobos@,
Still we are able to reproduce the issue on latest Canary#58.0.3025.0 on Windows7,Mac 10.12.2 & Ubuntu-14.04.Please look into this issue & update the thread accordingly.
Thank you.

ecobos@ I still cannot see any mails in the www-style archive. I did get the mail, though.

Seems like someone went through the pending messages and posted them today? https://lists.w3.org/Archives/Public/www-style/2017Mar/0008.html

Still able to reproduce the issue on Win-10 using latest canary #59.0.3046.0.

ecobos@ - Friendly Ping...!!

Could you please have a look into this issue.

Thanks...!!

Two new acid3 regression bugs:
chromium  bug #718708  - acid3 test #23 failed
chromium  bug #718709  - acid3 test #25 failed

Issue 745257 has been merged into this issue.

See:

https://github.com/w3c/csswg-drafts/issues/695
https://lists.w3.org/Archives/Public/www-archive/2017Jul/0003.html