internal override void SetBorderStyle(IntPtr handle, FormBorderStyle border_style) {
Form form = Control.FromHandle (handle) as Form;
if (form != null && form.window_manager == null && (border_style == FormBorderStyle.FixedToolWindow ||
border_style == FormBorderStyle.SizableToolWindow)) {
form.window_manager = new ToolWindowManager (form);
}
RequestNCRecalc(handle);
}