As we extracted the logic for comment threads with Ie2713ebdb, we can
use it for attention set. There was also a corner case which wasn't
covered by the logic which was previously used. We add a test case for
it to avoid future regressions.
In AttentionSetIT, we also switched to a different approach for looking
up the ChangeData instance. That was necessary due to the different
types used in the new test but also had a different reason: There's
no guarantee that the ChangeData object returned by PushOneCommit.Result
is updated after the push happened. We skipped additional improvements
like looking up attention set updates via a cleaner/better way than a
ChangeData instance as that's much beyond the scope of this change.
Change-Id: I9d8091c3ad6575304de9a5698cb1c94e32421e7b
159e70fd80