In D3D, cache static vertex buffers to prevent wasteful recreation BUG=angleproject:197 Change-Id: I66cd10609b2edbcf12b99530eafe1727511fe515 Reviewed-on: https://chromium-review.googlesource.com/296503 Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Austin Kinross <aukinros@microsoft.com> Tested-by: Jamie Madill <jmadill@chromium.org>