R1:fabf36a8191d

add arc unit data to table of contents in diff view

Summary: title

Test Plan: viewed a diff and verified nothing barfed.

Reviewers: vrana, epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2026

Differential Revision: https://secure.phabricator.com/D3906