[ReactNative] Allow uploading native files (e.g. photos) and FormData via XMLHttpRequest

Libraries/JavaScriptAppEngine/Initialization/InitializeJavaScriptAppEngine.js

@@ -102,6 +102,7 @@ function setUpXHR() {
   // The native XMLHttpRequest in Chrome dev tools is CORS aware and won't
   // let you fetch anything from the internet
   GLOBAL.XMLHttpRequest = require('XMLHttpRequest');
+  GLOBAL.FormData = require('FormData');
 
   var fetchPolyfill = require('fetch');
   GLOBAL.fetch = fetchPolyfill.fetch;