Otherwise, some test flags don't work.

Change-Id: Iacf3930d0eec28e4d690cd382adbb2ecf866a0e2
Reviewed-on: https://go-review.googlesource.com/55615Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>