This patch adds the basic implementation of WaitableEvent and
WorkerTaskPool for multi-threaded tasks in Dawn (for example, the
multi-threaded implementation of CreateReady*Pipeline()).
BUG=dawn:529
TEST=dawn_unittests
Change-Id: Ibf84348f4c0f0d26badc19ae94cd536cef89d084
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/36360
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>
Jiawei Shao