Reland "Switch browser/extensions/api/system_storage/system_storage_api.[h|cc] to the TaskScheduler API"

This is a reland of 73d162eb24c9c7a6b7cf4b65bc0562ae0a4236d9

It wasn't the culprit, https://chromium-review.googlesource.com/c/585386/ is.

Original change's description:
> Switch browser/extensions/api/system_storage/system_storage_api.[h|cc] to the TaskScheduler API
> 
> BUG=689520
> 
> Change-Id: Ia07f6c50a4dd0df96a63194e78a4cda85df181c6
> Reviewed-on: https://chromium-review.googlesource.com/586467
> Commit-Queue: Gabriel Charette <gab@chromium.org>
> Reviewed-by: Gabriel Charette <gab@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#490406}

TBR=ningxin.hu@intel.com

Bug: 689520
Change-Id: I3d1bfa52dd89bbd9b9c6c512c413512bcc91dda0
Reviewed-on: https://chromium-review.googlesource.com/591934
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#490569}
5 files changed