This should fix NaCl build failure for CL 49530.

Change-Id: Id9a54f0c81b1b5db5b5efb12a2ad6509c4ab42b3
Reviewed-on: https://go-review.googlesource.com/55770Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>