Refactoring change only. Found when working on multithreading CLs.

Bug: angleproject:2464
Change-Id: Ide91c7134b5f565e2f122a50cf92a4938189704a
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1825444Reviewed-by: Tim Van Patten <timvp@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>