GitLab

Add a BackgroundSync delegate to let components embedder customize the
logic in components/background_sync.

Use this delegate to customize UKM logging logic, and remove the
dependency on UkmBackgroundService from BackgroundSyncControllerImpl,
which will eventually be moved to components.

background_sync_metrics* will be moved to components/ in a follow-up CL.

Bug: 1087486
Change-Id: Ia6221f9db842ba8a2da90a1ef3fe721bc113b858
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2443089Reviewed-by: Brian White <bcwhite@chromium.org>
Reviewed-by: Rayan Kanso <rayankans@chromium.org>
Commit-Queue: Mugdha Lakhani <nator@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814301}