How to close Tab of IE running XBAP Application, not the whole browser?

privatevoid button1_Click(object sender, RoutedEventArgs e)
    {
      WindowInteropHelper wih = new WindowInteropHelper(Application.Current.MainWindow);
      IntPtr ieHwnd = GetAncestor(wih.Handle, 2 /*GA_ROOT*/);
      PostMessage(ieHwnd, 0x10/*WM_CLOSE*/, IntPtr.Zero, IntPtr.Zero);   
    } 

    [DllImport("user32", ExactSpelling = true, CharSet = CharSet.Auto)]privatestaticextern IntPtr GetAncestor(IntPtr hwnd, int flags); 

    [DllImport("user32", CharSet = CharSet.Auto)]privatestaticexternbool PostMessage(IntPtr hwnd, int msg, IntPtr wparam, IntPtr lparam);