See #15604.  This was a bug in a CL that has since been
rolled back.  Adding a test to challenge the next attempter.

Change-Id: Ic43be254ea6eaab0071018cdc61d9b1c21f19cbf
Reviewed-on: https://go-review.googlesource.com/23000Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>