Summary: Ref T5568. As discussed in IRC. This is very rough and not widely useable, but represents a solid first step.
Test Plan: Ran `arc unit` with a bunch of flags.
Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: rfreebern, aripringle, jaydiablo, BYK, tycho.tatitscheff, epriestley, Korvin
Maniphest Tasks: T5568
Differential Revision: https://secure.phabricator.com/D13579
