HTTP backend used by the Http service that delegates to dart:html's HttpRequest and deals with Dart bugs.

Never use this service directly, instead use the higher-level Http.

During testing this implementation is swapped with MockHttpBackend which can be trained with responses.

class HttpBackend {
 /**
  * Wrapper around dart:html's [HttpRequest.request]
  */
 async.Future request(String url,
     {String method, bool withCredentials, String responseType,
     String mimeType, Map<String, String> requestHeaders, sendData,
     void onProgress(dom.ProgressEvent e)}) {
   // Complete inside a then to work-around dartbug.com/13051
   var c = new async.Completer();

   dom.HttpRequest.request(url,
       method: method,
       withCredentials: withCredentials,
       responseType: responseType,
       mimeType: mimeType,
       requestHeaders: requestHeaders,
       sendData: sendData,
       onProgress: onProgress).then((x) => c.complete(x));
   return c.future;
 }
}