Updates golang/go#24440.

Change-Id: Idbe22ca853ea4771bb979782ef3bac8b03c59b87
Reviewed-on: https://go-review.googlesource.com/63998
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>