Chromium change:

https://chromium.googlesource.com/chromium/src/+/89a5f3ab57a994cd2652c45475c4b83895a40a94

commit 89a5f3ab57a994cd2652c45475c4b83895a40a94
Author: John Abd-El-Malek <jam@chromium.org>
Date:   Fri Jun 14 18:21:53 2019 +0000

    Remove IOThread class as it's not needed anymore.

    Bug: 934009