The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1a291743ecb7ee844ef19a10817443a4a66fb4cf

commit 1a291743ecb7ee844ef19a10817443a4a66fb4cf
Author: Guido Urdaneta <guidou@chromium.org>
Date: Thu May 10 18:32:32 2018

Set the main thread of the audio process as type UI on Mac

This ensures that the main thread as a CFRunLoop, which is required
by audio APIs on Mac.

Bug:  841845 
Change-Id: I10be74d77c1585014a63896099eb2b4acb5b345b
Reviewed-on: https://chromium-review.googlesource.com/1054227
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Olga Sharonova <olka@chromium.org>
Reviewed-by: Olga Sharonova <olka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557597}
[modify] https://crrev.com/1a291743ecb7ee844ef19a10817443a4a66fb4cf/chrome/browser/chrome_content_browser_client.cc