From main repo: https://go-review.googlesource.com/#/c/6350
                https://go-review.googlesource.com/#/c/6385

Change-Id: Ieba5ff60fc501be9aa4739860c8fe026f8b3eb67
Reviewed-on: https://go-review.googlesource.com/8721Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>