Move QueueEnabledVoter to TaskQueue

Simplify implementation of TaskQueueImpl and remove its dependency on
TaskQueue. This will be needed as we make TaskQueue not refcounted and
the base class of TaskQueueImpl.

Eventually we might also get rid of QueueEnabledVoter entirely and this
patch would make that easier too.

Bug: 891670
Change-Id: I8064394e59fd112fcded66790b49547eccf6226c
Reviewed-on: https://chromium-review.googlesource.com/c/1454587
Commit-Queue: Carlos Caballero <carlscab@google.com>
Reviewed-by: Alex Clarke <alexclarke@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#629647}
5 files changed