Add InternalContentCapture Task Type

ContentCaptureTask will run in Idle task queue and has the fixed
BestEffortPriority.
- This patch added BestEffortTaskQueue which has fixed BestEffortPriority.
- ContentCapture task run in BestEffortTaskQueue.

Bug: 924681
Change-Id: Iac93a983b4b82495e1e8e8f59be3677eaf9458c4
Reviewed-on: https://chromium-review.googlesource.com/c/1435840
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: Tao Bai <michaelbai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629417}
8 files changed