This D3D-only class has one method, used to generate the D3D
IndexBuffer/VertexBuffer. This can help us mock up
IndexDataManager.

At a later point we can refactor the VertexFormat queries
from Renderer into a Caps struct that mirrors our Texure
Caps.

BUG=angleproject:956

Change-Id: Id8b1220a763873ee871ce92365bbee03633789c7
Reviewed-on: https://chromium-review.googlesource.com/262774Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>