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Summary:
Show line count, arcanist project and base revision.

This adds a little clutter but I think we're still okay and I can play around
with it later.

Test Plan: Looked at a couple of revisions. I'm actually not 100% sure about the
SVN logic but maybe I will test that before committing.
Reviewed By: tomo
Reviewers: tomo, jungejason, tuomaspelkonen, aran
CC: aran, tomo
Differential Revision: 685