How to download page source (HTML) in Windows Phone

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Windows

phone

I am creating a youtube video downloader for windows phone. Why I am not able to download page source (HTML) of youtube. My Code is:

private void Button_Click_1(object sender, RoutedEventArgs e)
        {
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://www.youtube.com");
            request.BeginGetResponse(new AsyncCallback(MyFun), request);
        }

        public void MyFun(IAsyncResult result)
        {
            HttpWebRequest request = (HttpWebRequest)result.AsyncState;

            WebResponse response = request.EndGetResponse(result);

            string data = "";
   using (Stream stream = response.GetResponseStream())
            {
                StreamReader reader = new StreamReader(stream);

                data = reader.ReadToEnd();
            }
        }

It works fine when I use google.com or any other url except youtube.com