Add PyTorchPredictorContainer (#15899)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15899
Add PyTorchPredictorContainer to support multiple jit script modules
Reviewed By: pritamdamania87
Differential Revision: D13596139
fbshipit-source-id: 3ce0bdf2f4dbba7aa1d20e824d03e5ac98f5d887
