Updates #16937

Change-Id: I6d1b210c741269b58040bd68bf3b51644f891737
Reviewed-on: https://go-review.googlesource.com/28487
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>