Additional fix for link task worker pool race See [1] for context. While that change fixed the race condition, it was not great that the task held on to the worker pool for so long. This change avoids the race condition as well by releasing the worker pool as soon as the link task has no further use for it. [1]:https://chromium-review.googlesource.com/c/angle/angle/+/5428806 Bug: angleproject:8661 Change-Id: Ibcbad0afe518e649a63dfdf938bd566c8f80e368 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5431154 Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Roman Lavrov <romanl@google.com> Commit-Queue: Roman Lavrov <romanl@google.com> Auto-Submit: Shahbaz Youssefi <syoussefi@chromium.org>