Updates golang/go#24440.

Change-Id: Ic56bb1add57831d6c94f148d209417be5aa22cb2
Reviewed-on: https://go-review.googlesource.com/63996
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>