Remove the blocking pool from the service process.

The blocking pool is deprecated.

The only remaining user was the ServiceProcessPrefs' JsonPrefStore,
which now uses TaskScheduler instead.

Bug: 667892
Change-Id: Ic4739018ff111b7886bbc186e50f40408a8d9367
Reviewed-on: https://chromium-review.googlesource.com/660677
Reviewed-by: Gene Gutnik <gene@chromium.org>
Commit-Queue: Francois Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501264}
2 files changed