是不是调用OnSize，MFC系统就会调用MoveWindow函数，而不需要再另外调用了呢？
说反了，调用MoveWindow会触发wm_size消息，从而触发onsize函数
MoveWindow sends the WM_WINDOWPOSCHANGING, WM_WINDOWPOSCHANGED, WM_MOVE, WM_SIZE, and WM_NCCALCSIZE messages to the window.