Implement wxNotebook::CalcSizeFromPage() for wxGTK.

The implementation is far from perfect as it relies on hard-coded margins but
is better than nothing as it allows wxNotebook best size determination and
SetPageSize() method to work correctly.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70112 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

samples/notebook/notebook.h

@@ -52,6 +52,8 @@ public:
     void OnNextPage(wxCommandEvent& event);
     void OnChangeSelection(wxCommandEvent &event);
     void OnSetSelection(wxCommandEvent &event);
+    void OnGetPageSize(wxCommandEvent &event);
+    void OnSetPageSize(wxCommandEvent &event);
 
     void OnAddSubPage(wxCommandEvent& event);
     void OnAddPageBefore(wxCommandEvent& event);
@@ -167,6 +169,8 @@ enum ID_COMMANDS
     ID_ADD_SUB_PAGE,
     ID_CHANGE_SELECTION,
     ID_SET_SELECTION,
+    ID_GET_PAGE_SIZE,
+    ID_SET_PAGE_SIZE,
 
 #if wxUSE_HELP
     ID_CONTEXT_HELP,