The D3D-specific code we can split into D3D-only methods, and the GL-level shared code we can place in Program instead of making Impl methods. This cleans up the Impl inteface significantly. BUG=angleproject:1123 Change-Id: Ibcb7d07733eb939adf5bb4f5395a661875a60238 Reviewed-on: https://chromium-review.googlesource.com/293763Reviewed-by: Corentin Wallez <cwallez@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>
