Updates golang/go#13372.

Change-Id: I623de97eb19880356148cbcb7d17759df82684aa
Reviewed-on: https://go-review.googlesource.com/24751
Run-TryBot: Mikio Hara <mikioh.mikioh@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>