title: Not able to send post parameter by request builder
body: <p>It is opening new window but not passing Post parameters to new window using GWT.</p>
  
  <pre><code>final RequestBuilder rb = new RequestBuilder(RequestBuilder.POST, encodedUrl);
  rb.setHeader("Content-type", "application/x-www-form-urlencoded");
  rb.setRequestData(json);
  Request response = rb.sendRequest(json.toString(), new RequestCallback() {
      public void onError(Request request, Throwable exception) {}
      public void onResponseReceived(Request request, Response response) {
          Window.open(rb.getUrl(), postTarget, postWinFeatures);
      }
  });
  </code></pre>