Add batch id to tracer event (#21446)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21446
this is used for easier tracing of iter id when looking at trace diagram
Reviewed By: ilia-cher
Differential Revision: D15628950
fbshipit-source-id: ee75b3bdb14a36abc18c7bddc49d8ec9789b724d
