implemented a simple DoGetBestSize() for MSW's wxScrollBar

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@26677 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/scrolbar.h

@@ -60,6 +60,9 @@ public:
                              WXWORD pos, WXHWND control);
 
 protected:
+
+    wxSize DoGetBestSize() const;
+
     int m_pageSize;
     int m_viewSize;
     int m_objectSize;