Refactor WorkerThreadScheduler unit tests.

Bug: 841735
Change-Id: I86007d80dd719cd00c4b224d9f88479daa1bb422
Reviewed-on: https://chromium-review.googlesource.com/1101019
Reviewed-by: Alexander Timin <altimin@chromium.org>
Commit-Queue: Greg Kraynov <kraynov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567263}
1 file changed