Update #12563.

Change-Id: Id87f8e53586accd662575c31961c39787268df7a
Reviewed-on: https://go-review.googlesource.com/14471
Run-TryBot: Minux Ma <minux@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Dave Cheney <dave@cheney.net>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>