For #6957

Change-Id: Ic497c12f33efc933e9fe81f6cd1b2a0a01abbabf
Reviewed-on: https://go-review.googlesource.com/19820
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>