Called by Create to access the window class information.
By default, CWindowImpl obtains this method through the DECLARE_WND_CLASS macro, which specifies a new window class.
To superclass an existing window class, derive your class from CWindowImpl and include the DECLARE_WND_SUPERCLASS macro to override GetWndClassInfo. For more information, see the CWindowImpl overview.
Besides using the DECLARE_WND_CLASS and DECLARE_WND_SUPERCLASS macros, you can override GetWndClassInfo with your own implementation.