I don't know why it is not working.  Filed issue 19111 for this.

Fixes build.

Update #19111.

Change-Id: I76f8d6aafba5951da2f3ad7d10960419cca7dd1f
Reviewed-on: https://go-review.googlesource.com/37092Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>