This was fixed long ago but the test was not enabled.

For #8189.

Change-Id: Ia44ef752b6bf076f3e243d2d0db326a392a20193
Reviewed-on: https://go-review.googlesource.com/27310
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>