My local bisect indicates that crrev.com/c/1159335 is the culprit.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7a07960a925b2b0c2e8dc5e9b49f349fb5bd3e7a

commit 7a07960a925b2b0c2e8dc5e9b49f349fb5bd3e7a
Author: Kunihiko Sakamoto <ksakamoto@chromium.org>
Date: Fri Aug 03 05:19:12 2018

Revert "chrome: Call SetUpBundleOverrides from ChromeMain."

This reverts commit 381beab379e4243ece5610862be54367b2ed4dd6.

Reason for revert: Suspected of breaking browser_tests on Mac. crbug.com/870579

Original change's description:
> chrome: Call SetUpBundleOverrides from ChromeMain.
> 
> It looks like we always need to call SetUpBundleOverrides no matter
> what the process type is, so we can just call it from ChromeMain. This
> will save us from needing to call this function from browser-specific
> code in a later change.
> 
> While here, also remove a dead declaration.
> 
> Bug: 855193
> Change-Id: I449d92ef9c7d80d066d4cfefb3015014bd407cc1
> Reviewed-on: https://chromium-review.googlesource.com/1159335
> Reviewed-by: Robert Sesek <rsesek@chromium.org>
> Reviewed-by: Avi Drissman <avi@chromium.org>
> Commit-Queue: Avi Drissman <avi@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#580285}

TBR=avi@chromium.org,pcc@chromium.org,rsesek@chromium.org,mark@chromium.org

Change-Id: I32f905ff8f82306a85fbc9798652b8c99aa46009
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 855193,870579
Reviewed-on: https://chromium-review.googlesource.com/1161722
Reviewed-by: Kunihiko Sakamoto <ksakamoto@chromium.org>
Commit-Queue: Kunihiko Sakamoto <ksakamoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580456}
[modify] https://crrev.com/7a07960a925b2b0c2e8dc5e9b49f349fb5bd3e7a/chrome/app/chrome_main.cc
[modify] https://crrev.com/7a07960a925b2b0c2e8dc5e9b49f349fb5bd3e7a/chrome/app/chrome_main_delegate.cc
[modify] https://crrev.com/7a07960a925b2b0c2e8dc5e9b49f349fb5bd3e7a/chrome/app/chrome_main_mac.h

The revert fixed the issue for now, assigning the CL author for perma-fix.

 Issue 870642  has been merged into this issue.

 Issue 870684  has been merged into this issue.