Serialize XLA Tensor (#27041)
Summary:
https://github.com/pytorch/pytorch/issues/25882
Reopening both PRs to master/v1.3.0 to save myself from rebase hell...
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27041
Differential Revision: D17676345
Pulled By: ailzhang
fbshipit-source-id: 4784c9f8f0723cd3ff081af3336e672812aaad14
