Summary:
XMLHttpRequest was sending the request before registering any listeners, resulting in a warning from the native event emitter.
Since we weren't seeing widespread problems with XHR missing data, this was probably working OK in practice because the queuing of events meant that the listener would have been registered before the message was actually delivered.
Still, this was working more through luck than design. This diff fixes it by registering the listeners *before* sending the request.
Reviewed By: lexs
Differential Revision: D3371320
fbshipit-source-id: c688d4053a61f856eaacccd0106905edbefcc86a
bdcdfb03d4