backported ClientToWindowSize(), WindowToClientSize() to 2.8

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@52330 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/window.h

@@ -326,6 +326,12 @@ public:
         return wxRect(GetClientAreaOrigin(), GetClientSize());
     }
 
+#if wxABI_VERSION >= 20808
+    // client<->window size conversion
+    wxSize ClientToWindowSize(const wxSize& size) const;
+    wxSize WindowToClientSize(const wxSize& size) const;
+#endif
+
         // get the size best suited for the window (in fact, minimal
         // acceptable size using which it will still look "nice" in
         // most situations)