Updates #15228.

Change-Id: Iefdffa146703ee1c04afc2b71d9de1f0a0811f86
Reviewed-on: https://go-review.googlesource.com/32146
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>