This fixes the compile on OSX.

BUG=angle:773

Change-Id: I68111e178986bb78b73006a1559ba26120275599
Reviewed-on: https://chromium-review.googlesource.com/238441Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>