GitLab

Update the FileReader class to use the new task scheduling API, as well
as the dedicated Extensions-related file task runner.

Bug: 689520
Bug: 750122
Change-Id: I3dd119e9c6bc368ab0186e599a4a67df02b872d6
Reviewed-on: https://chromium-review.googlesource.com/594010
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491566}