This fixes compile errors on OSX.

BUG=angle:773

Change-Id: I11ce9fd470a54b08656a62afc50586e5d2f987d8
Reviewed-on: https://chromium-review.googlesource.com/238446Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>