Back out "Revert D13596031: Improve c2-aten tensor interop and add proper testing" (#16514)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16514
Original commit changeset: dc371697f14b
Relanding https://github.com/pytorch/pytorch/pull/15860 - the problem was that layer_norm was using at::empty which is not yet on mobile
Reviewed By: ezyang
Differential Revision: D13861480
fbshipit-source-id: e2116da32bc117175c96b9151b1beba9b31eff36
