This is Regression Issue broken in M-63 and and Using the per-revision bisect providing the bisect results.
Good Build: 63.0.3213.0 (Revision:501133).
Bad Build: 63.0.31214.0 (Revision:501490).

You are probably looking for a change made after 501393 (known good), but no later than 501394 (first known bad).

CHANGELOG URL:

The script might not always return single CL as suspect as some perf builds might get missing due to failure.

https://chromium.googlesource.com/chromium/src/+log/6a21639f7b4d135d70c4f664a261dc379a41477c..673e8a437f569bff9705e9b6e9883d25b795d384

Suspect: https://chromium.googlesource.com/chromium/src/+/673e8a437f569bff9705e9b6e9883d25b795d384

@dschuyler: Could you please look into the issue, pardon me if it has nothing to do with your changes and if possible please assign it to concern owner.

Note:
In Mac OS(10.11.6, 10.12.3, 10.12.5) font size for 'Customize Fonts' appears small even without changing font size to Very Large.

Adding RB Label as this is a recent Regression. Please remove if not required.
Thank You.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/49684282e5a1536d55af2ba4934931eaf6c59272

commit 49684282e5a1536d55af2ba4934931eaf6c59272
Author: Dave Schuyler <dschuyler@chromium.org>
Date: Thu Sep 14 02:54:11 2017

[cr webui] set font size on cr-link-row

This CL sets the font size to 100% on a link row. This addresses two issues:
- The overridden Mac specific size of 11px is set back to the MD settings 
  default of 13px.
- On desktop (mac and non-mac) the font size will follow the custom font
  size selected by the user.

Bug:  764942 ,  764608 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ice9404cea6c1303f60e96babd72c354f85596594
Reviewed-on: https://chromium-review.googlesource.com/666219
Reviewed-by: Scott Chen <scottchen@chromium.org>
Commit-Queue: Dave Schuyler <dschuyler@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501852}
[modify] https://crrev.com/49684282e5a1536d55af2ba4934931eaf6c59272/ui/webui/resources/cr_elements/cr_link_row/cr_link_row.html

Retested the above issue on Latest Canary #63.0.3216.0 on Win(7,8,10),Mac(10.11.6, 10,12.3, 10,12,5), Linux(14.04 LTS)
and Fix is working as intended.

Deleted: Current_Result.png 225 KB

	Current_Result.png 225 KB View Download

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5384a06769acea83ddb7dd38b85888fceaecf7f6

commit 5384a06769acea83ddb7dd38b85888fceaecf7f6
Author: Dave Schuyler <dschuyler@chromium.org>
Date: Fri Sep 15 20:52:08 2017

[cr webui] set font size on cr-link-row

This CL sets the font size to 100% on a link row. This addresses two issues:
- The overridden Mac specific size of 11px is set back to the MD settings 
  default of 13px.
- On desktop (mac and non-mac) the font size will follow the custom font
  size selected by the user.

Bug:  764942 ,  764608 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: Ice9404cea6c1303f60e96babd72c354f85596594
Reviewed-on: https://chromium-review.googlesource.com/666219
Reviewed-by: Scott Chen <scottchen@chromium.org>
Commit-Queue: Dave Schuyler <dschuyler@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#501852}(cherry picked from commit 49684282e5a1536d55af2ba4934931eaf6c59272)
Reviewed-on: https://chromium-review.googlesource.com/669619
Reviewed-by: Dave Schuyler <dschuyler@chromium.org>
Cr-Commit-Position: refs/branch-heads/3202@{#263}
Cr-Branched-From: fa6a5d87adff761bc16afc5498c3f5944c1daa68-refs/heads/master@{#499098}
[modify] https://crrev.com/5384a06769acea83ddb7dd38b85888fceaecf7f6/ui/webui/resources/cr_elements/cr_link_row/cr_link_row.html

 Issue 765601  has been merged into this issue.