Use TaskScheduler instead of SequencedWorkerPool in blockfile cache.

This CL migrates calls from SequencedWorkerPool to TaskScheduler in
the posix blockfile cache. The calls were already redirected to
TaskScheduler under the hood (via
EnableWithRedirectionToTaskSchedulerForProcess).

Bug: 667892
Change-Id: I8abdb3df6d0fc4b35ad96109c8af818828a4df79
Reviewed-on: https://chromium-review.googlesource.com/850754
Commit-Queue: François Doray <fdoray@chromium.org>
Reviewed-by: Josh Karlin <jkarlin@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#528385}
2 files changed