Exposing LengthsSum/Mean/Max in pytorch (#20802)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20802
Need this for sequence model
Reviewed By: dzhulgakov
Differential Revision: D15448529
fbshipit-source-id: cd5abe3b689fc0e02feff10faf8cd61c99369f4f
