Closes #15815

Change-Id: I08154dbff416198cf7787e446b1e00e62c03a972
Reviewed-on: https://go-review.googlesource.com/30917Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>