Updates golang/go#18326

Change-Id: Iaed30073bab10c7fc25132b388d7b2fc101293d5
Reviewed-on: https://go-review.googlesource.com/34494Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>