Passes go test -race.

Change-Id: I14b5b1b1a8ad1e43d60013823d71d78a6519581f
Reviewed-on: https://go-review.googlesource.com/37588
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>