In a previous fix to a Clang build error, we had neglected to update
the GN build. Broken in commit 07d49ef5.

BUG=angle:707

Change-Id: Ic11aa907d591540e915bec60f3bafaea471689d5
Reviewed-on: https://chromium-review.googlesource.com/210652Tested-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Brett Wilson <brettw@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>