把消息送到默认窗口函数里，并非一点用都没有，可能会产生新的消息（以WM_WINDOWPOSCHANGED为例）

procedure TForm1.Button1Click(Sender: TObject);
begin
  panel1.Left:=panel1.Left-10;
end;

procedure TWinControl.WMWindowPosChanged(var Message: TWMWindowPosChanged);
var
  Framed, Moved, Sized: Boolean;
begin
  Framed := FCtl3D and (csFramed in ControlStyle) and (Parent <> nil) and (Message.WindowPos^.flags and SWP_NOREDRAW = 0);
  Moved := (Message.WindowPos^.flags and SWP_NOMOVE = 0) and IsWindowVisible(FHandle); // API
  Sized := (Message.WindowPos^.flags and SWP_NOSIZE = 0) and IsWindowVisible(FHandle);
  if Framed and (Moved or Sized) then InvalidateFrame;  
  // if not (csDestroyingHandle in ControlState) then UpdateBounds; // 屏蔽这句
  inherited; 

  if Framed and ((Moved or Sized) or (Message.WindowPos^.flags and (SWP_SHOWWINDOW or SWP_HIDEWINDOW) <> 0)) then
    InvalidateFrame; // 类函数，简单调用API
end;

procedure TWinControl.DefaultHandler(var Message);
begin
   Result := CallWindowProc(FDefWndProc, FHandle, Msg, WParam, LParam); 
end;