Summary:
This was supposed to be an update to D1720014 but I screwed up with arc.

Test Plan: run the test by hand and see the output

Reviewed By: jsedgwick@fb.com

Subscribers: exa, njormrod, folly-diffs@

FB internal diff: D1721951

Signature: t1:1721951:1417801009:72a27ec2ca473a996785ff9cae48bd51a43d9045