Enable postSubBuffer on D3D11 with DXGI 1.2. BUG=147291 Change-Id: Iafddb83b4949168f1c59272a99ae0244d86ce3f9 Reviewed-on: https://chromium-review.googlesource.com/270572 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Sunny Sachanandani <sunnyps@chromium.org>