Passes toolstash -cmp.

Change-Id: I05322fb5afd213f13fb247ec1a5f655c17a58774
Reviewed-on: https://go-review.googlesource.com/20522
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>