Code review comment for lp:~afrantzis/mir/fix-1511798-alternative

I think the right solution is to move the "session->destroy_surface(surface);" call from AbstractShell::destroy_surface() to <Policy>::handle_delete_surface(). (There are four of these, plus DefaultWindowManager::remove_surface() in playground.)

It seems like a PITA, but this allows the window management policy control over the point at which the surface and decorations are destroyed.