[EoS] Enable scheduling the daily catalog update task.

- The ExploreSitesService is configured to start on startup if the
  feature is enabled, and will schedule the daily task directly in the
  service factory.
- The task will cancel itself if it runs and the feature is disabled.

Bug: 867488
Change-Id: I38b55c97d9b2d26a3c94cdff5bcce03bf341d404
Reviewed-on: https://chromium-review.googlesource.com/1244738
Commit-Queue: Justin DeWitt <dewittj@chromium.org>
Reviewed-by: Dmitry Titov <dimich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594726}
8 files changed