Includes a fix necessary for multithreading tests.

Bug: angleproject:2464
Change-Id: I009e48be611ef7b96ad9caba8e0729881e1a8fb9
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1872789Reviewed-by: Tobin Ehlis <tobine@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>