Passes toolstash -cmp.

Change-Id: Id16009ef3ef1173eafe0f0c578dbf325b61aab3c
Reviewed-on: https://go-review.googlesource.com/20674
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>
TryBot-Result: Gobot Gobot <gobot@golang.org>