GitLab

Pass through the Abort message to the DownloadService for any
outstanding downloads matching the given job_unique_id.

Update abort unit tests to verify that the download successful messages
do not get delivered.

Change-Id: I600a3f102047939d7189dc6d30e9ca88eedf4c04
Bug: 758562
Reviewed-on: https://chromium-review.googlesource.com/723321Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: John Mellor <johnme@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#510090}