Show broken units in revision history

Summary:
This is hacky, and I'm not sure I'm happy with it; Until T9365 is done, this will show up
broken tests with an appropriate star in the Revision History.

Test Plan: Created 1M messages in a couple of old diffs in a revision. The query took ~80us (On SSD drive).

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D16483