Summary:
In the Docs of `NSURLSession` ,
>IMPORTANT
>The session object keeps a strong reference to the delegate until your app exits or explicitly >invalidates the session. If you do not invalidate the session, your app leaks memory until it exits.
The RCTMultipartDataTask will cause memory leaks, it will make `RCTBatchedBridge` and ` RCTMultipartDataTask` will not release.
So call `[session finishTasksAndInvalidate];` at the end of `startTask` function.
Closes https://github.com/facebook/react-native/pull/12673
Reviewed By: shergin
Differential Revision: D4896497
Pulled By: javache
fbshipit-source-id: eb5f8761f67ad33a7de081a68a9a7e1d4329bfc0
47f834a76d