Below is manual regression range:

Good build: 61.0.3160.0
Bad build: 61.0.3161.0

Note: Issue is also reproducible on Linux (14.04 LTS)and Mac OS X(10.11.6,10.12.3) OS.

Kindly review the attached screen-cast for reference.

Deleted: Overlay_Screenshot.png 24.3 KB

	Overlay_Screenshot.png 24.3 KB View Download

Deleted: Actual behavior.mp4 823 KB

	Actual behavior.mp4 823 KB View Download

Deleted: Expected behavior.mp4 684 KB

	Expected behavior.mp4 684 KB View Download

Able to reproduce the issue on Windows 7 using chrome latest canary-61.0.3161.0.
Manual bisect info:
------------------
Good build: 61.0.3160.0-Revision-487322
Bad build: 61.0.3161.0-Revision-487694

Per revision bisect info:
------------------------
You are probably looking for a change made after 487677 (known good), but no later than 487678 (first known bad).
CHANGELOG URL:
The script might not always return single CL as suspectas some perf builds might get missing due to failure.
https://chromium.googlesource.com/chromium/src/+log/993d5a05009d3576e58e0f88b9159b0c2fea7031..03a5bd08a162540c03eb00b3b6e275e582d2f3ec

Possible suspect:
----------------
https://chromium.googlesource.com/chromium/src/+/03a5bd08a162540c03eb00b3b6e275e582d2f3ec

dschuyler@Could you please take a look & reassign to the right owner if it is not related to your change.

As it is regressed recently,marking it as Release block stable.
Thanks..!!

Test: fyi the gray separator line is also missing on the reset profile dialog at chrome://settings/resetProfileSettings and the clear browsing data dialog at chrome://settings/clearBrowsingData. Please check that all three will have a separator line with this fix.

CL at https://chromium-review.googlesource.com/c/578375

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/80f42ed65b2efec437ac51c31ebcc782dae85328

commit 80f42ed65b2efec437ac51c31ebcc782dae85328
Author: Dave Schuyler <dschuyler@chromium.org>
Date: Fri Jul 21 03:01:13 2017

[MD settings] style dialog footer with separator line

This CL correct dialog footer styling so that a footer will have a gray
separator line consistently.

Bug:  746186 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I1822f3724762f07658404ed03772d2bb8a83e507
Reviewed-on: https://chromium-review.googlesource.com/578375
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Dave Schuyler <dschuyler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488564}
[modify] https://crrev.com/80f42ed65b2efec437ac51c31ebcc782dae85328/chrome/browser/resources/settings/people_page/people_page.html
[modify] https://crrev.com/80f42ed65b2efec437ac51c31ebcc782dae85328/chrome/browser/resources/settings/reset_page/reset_profile_dialog.html
[modify] https://crrev.com/80f42ed65b2efec437ac51c31ebcc782dae85328/ui/webui/resources/cr_elements/cr_dialog/cr_dialog.html

[Auto-generated comment by a script] We noticed that this issue is targeted for M-61; it appears the fix may have landed after branch point, meaning a merge might be required. Please confirm if a merge is required here - if so add Merge-Request-61 label, otherwise remove Merge-TBD label. Thanks.

Your change meets the bar and is auto-approved for M61. Please go ahead and merge the CL to branch 3163 manually. Please contact milestone owner if you have questions.
Owners: amineer@(Android), cmasso@(iOS), ketakid @(ChromeOS), govind@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Pls merge your change to M61 branch 3163 by 5:00 PM PT, Monday (07/24) so we can take it in for next week M61 dev release. Thank you.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4c17c8d79cff52b7bbde8cb30b182667b89875b7

commit 4c17c8d79cff52b7bbde8cb30b182667b89875b7
Author: Dave Schuyler <dschuyler@chromium.org>
Date: Mon Jul 24 21:46:10 2017

[MD settings] style dialog footer with separator line

This CL correct dialog footer styling so that a footer will have a gray
separator line consistently.

TBR=dschuyler@chromium.org

(cherry picked from commit 80f42ed65b2efec437ac51c31ebcc782dae85328)

Bug:  746186 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I1822f3724762f07658404ed03772d2bb8a83e507
Reviewed-on: https://chromium-review.googlesource.com/578375
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Dave Schuyler <dschuyler@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#488564}
Reviewed-on: https://chromium-review.googlesource.com/583936
Reviewed-by: Dave Schuyler <dschuyler@chromium.org>
Cr-Commit-Position: refs/branch-heads/3163@{#15}
Cr-Branched-From: ff259bab28b35d242e10186cd63af7ed404fae0d-refs/heads/master@{#488528}
[modify] https://crrev.com/4c17c8d79cff52b7bbde8cb30b182667b89875b7/chrome/browser/resources/settings/people_page/people_page.html
[modify] https://crrev.com/4c17c8d79cff52b7bbde8cb30b182667b89875b7/chrome/browser/resources/settings/reset_page/reset_profile_dialog.html
[modify] https://crrev.com/4c17c8d79cff52b7bbde8cb30b182667b89875b7/ui/webui/resources/cr_elements/cr_dialog/cr_dialog.html

Rechecked this issue on Windows 10 and Mac 10.11.6 OS using chrome version 61.0.3163.13 and fix is working as expected i.e. Horizontal separator line is seen on 'Sign out of Chrome' overlay

Attaching screen-cast for the same.

Deleted: 61.0.3163.13_ behavior.mp4 835 KB

	61.0.3163.13_ behavior.mp4 835 KB View Download

Retested this issue on Linux 14.04 OS using build #61.0.3163.13 and fix is working as intended.