Under Windows only, sets the window to be used as a toolbar for this MDI parent window. It is necessary since wxWindows does not provide general functionality for application management of an MDI client area.
When the frame is resized, the toolbar is resized to be the width of the frame client area, and the toolbar height is kept the same.
The parent of the toolbar must be this frame, which must itself have been created as an MDI parent frame.
Please note that SDI frames and MDI child windows must have their toolbars managed by the application.