Obviously D3D-only class is obvious. :)

BUG=angle:731

Change-Id: Ide54e76a8b9bacb9b6834e2cb0a801140eecfe46
Reviewed-on: https://chromium-review.googlesource.com/213862Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Brandon Jones <bajones@chromium.org>