virtual void HandleMouseDown(BPoint point, int32 hitTestArea, int32 buttons, int32 clicks);
Remarks
If the mouse is over the close box, the close box is pressed. But the view is
only closed if the mouse is still over the close box, if the mouse button is going up.
If the mouse button is moved outside the close box rectangle while the mouse
button is pressed, the close box toggles its state. The same is true for the
maximize button.
CMDITitleMouseAction
