Summary:
@public
We're seeing crashes from multiple threads trying to call `[NSData appendData:]` at the same time. Usually the RCTURLRequestHandlers implementation avoids this but if you're using a background queue, it is pretty easy to reach this case.
Adding a lock to accessors of `_data` should prevent this.
Reviewed By: shergin
Differential Revision: D17552136
fbshipit-source-id: 3384d36221d0ada8cda638ad8e79e1bf3862f93f
Mehdi Mulani