Passes toolstash -cmp.

Change-Id: Id504e71ed1f23900e24a9aed25143c94f4d7d50c
Reviewed-on: https://go-review.googlesource.com/21899
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>