Updates #21856

Change-Id: I9baa51fe23e6dd2fcf9dd14f7acfaf7457571e1d
Reviewed-on: https://go-review.googlesource.com/66334
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Mikio Hara <mikioh.mikioh@gmail.com>