This CL is adding a WorkerPool delegate to allow an embedder to post task on a custom thread pool. The target for this code is Chromium. The plan is to post tasks into the Chromium ThreadPool. Related CLs: 1) [this] 2) https://chromium-review.googlesource.com/c/chromium/src/+/2231864 3) https://chromium-review.googlesource.com/c/angle/angle/+/2231710 Bug: chromium:1091259 Change-Id: Ib990b06d4672b6f859d04b97ac4311a7a80ef7a9 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2231708 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>
