Added at::Dimname (#21280)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21280
ghimport-source-id: 921848326e4828ffd422868be26c409c6490e1ab
Differential Revision: D15698516
Pulled By: zou3519
fbshipit-source-id: 502b9b019d51dd46327e6caf2af69aa520c70cb6
