onWindowRemoved  
  fun onWindowRemoved(connectFlags: <Error class: unknown class> = ConnectFlags(0u), handler: (window: Window) -> Unit): <Error class: unknown class>(source)
Emitted when a class@Gtk.Window is removed from application.
This can happen as a side-effect of the window being destroyed or explicitly through method@Gtk.Application.remove_window.
Parameters
connectFlags 
a combination of ConnectFlags
handler
the Callback to connect. Params: window the class@Gtk.Window that is being removed