Remove usages of GetBlockingPool in Pepper.

Bug: 667892
Change-Id: I715c7553a27a00b61af4cd3c686c86eaa528db9f
Reviewed-on: https://chromium-review.googlesource.com/543896
Reviewed-by: Raymes Khoury <raymes@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#482355}
1 file changed