R1:5485fb8aa9e7

Read modern coverage information for tables of contents

Summary:
Ref T8096. This modernizes the last thing which was reading the old datasource.

Also fix a bug where it didn't work.

Test Plan: {F698405}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T8096

Differential Revision: https://secure.phabricator.com/D13852