This error was introduced while fixing nits in the
previous CL.

The Delegate Pool was not created at all and always
fallback to the Async thread pool instead.

Bug: chromium:1091259
Change-Id: I5036836b5d792372636f21e936a03906eb587f67
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2262573Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Etienne Bergeron <etienneb@chromium.org>