Updates #13372.

Change-Id: Id2402a781474e9d0bb0901c5844adbd899f76cbd
Reviewed-on: https://go-review.googlesource.com/23123
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>