For #16360.

Change-Id: I99d1e5ab1f814f65b3066a498158a442f1bd477f
Reviewed-on: https://go-review.googlesource.com/31137
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>