如何使用Silverlight GET HttpWebRequest设置标头？

HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://example.com");
request.Method = "GET";

request.Headers["HeaderName"] = "HeaderValue";

HttpWebResponse response = (HttpWebResponse)request.GetResponse();
Stream responseStream = response.GetResponseStream();
StreamReader reader = new StreamReader(responseStream);
string responseData = reader.ReadToEnd();

response.Close();

using System;
using System.IO;
using System.Net;
using System.Windows;

namespace SilverlightHttpWebRequest
{
    public partial class MainPage : UserControl
    {
        public MainPage()
        {
            InitializeComponent();

            HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://example.com");
            request.Method = "GET";
            request.Headers["HeaderName"] = "HeaderValue";

            request.BeginGetResponse(new AsyncCallback(GetResponseCallback), request);
        }

        private void GetResponseCallback(IAsyncResult asynchronousResult)
        {
            HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
            HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asynchronousResult);

            Stream responseStream = response.GetResponseStream();
            StreamReader reader = new StreamReader(responseStream);
            string responseData = reader.ReadToEnd();

            Dispatcher.BeginInvoke(() =>
            {
                ResultTextBlock.Text = responseData;
            });

            response.Close();
        }
    }
}