Updates #15177

Change-Id: I748f025461f313b5b426821ead695f90d3011a6b
Reviewed-on: https://go-review.googlesource.com/21677Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>