For #13057.

Change-Id: Idbc50d5b08e055a23ab7cc9eb62dbc47b65b1815
Reviewed-on: https://go-review.googlesource.com/29050Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>