GitLab

The term "background" is confusing as it refers to a thread with a
specific priority. Use worker_pool instead to refer to
non-main-thread scheduler.

R=haraken@chromium.org,gab@chromium.org

Change-Id: Ia72090e39a3354cd14c539e64475cf661db15cd7
Reviewed-on: https://chromium-review.googlesource.com/c/1282396
Commit-Queue: Alexander Timin <altimin@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#630516}