public override async void Execute()
{
base.Execute();
HttpWebRequest httpWebRequest = WebRequest.CreateHttp(this.Url);
httpWebRequest.Method = "POST";
httpWebRequest.ContentType = string.Format("multipart/form-data; boundary={0}", this._boundary);
httpWebRequest.UserAgent = "2ch Browser (Windows Phone)";
var task = httpWebRequest.GetRequestStreamAsync();
await GetRequestStreamCallback(task, httpWebRequest);
}