Preserve log_dir arg and member for SummaryWriter (#20382)
Summary:
Given that tensorboardX and our PyTorch 1.1 release had `log_dir` as the argument for SummaryWriter initialization and member variable (which some users access), we need to preserve this name. However, we might deprecate this in the future and I've added a `get_logdir` method that can be used in the future.
cc natalialunova, lanpa
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20382
Reviewed By: NarineK
Differential Revision: D15300941
Pulled By: orionr
fbshipit-source-id: a29a70fcbc614a32ebfa6c655962fdff081af1af
