constructor(callback, retries) {
    apiclient.initialize();
    this.callback = callback;
    this.requestService = new EERequestService(!callback, retries);
  }
Prepares a call which will call the given callback from the handle()
method.

@param {function(?, string=)=} callback Callback to call.  If empty, the
    request will run in synchronous mode.
@param {number=} retries Overrides the default number of retries.