Passes toolstash -cmp.

Change-Id: I202b29495ca1aaf3c52879fa99fdc0a4b86703af
Reviewed-on: https://go-review.googlesource.com/36419
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>