Summary: Calling the event emitters on the main thread seems to be problematic, so let's dispatch it via the JS thread. This requires some changes to make "eventTarget" single-use because otherwise the binding would need to synchronize the actual JS call with the act of releasing the target.
Reviewed By: shergin
Differential Revision: D8375291
fbshipit-source-id: bd2b42731176ae209f4a19c232309c163fb1c01b