Merge branch 'grid-native-header-autosize'

Fixes for auto-sizing grid columns when using native header control.

Closes https://github.com/wxWidgets/wxWidgets/pull/1579

include/wx/generic/grid.h

@@ -2282,6 +2282,7 @@ protected:
     friend class wxGridWindow;
     friend class wxGridHeaderRenderer;
 
+    friend class wxGridHeaderColumn;
     friend class wxGridHeaderCtrl;
 
 private:
@@ -2404,6 +2405,8 @@ private:
                                    wxGridColLabelWindow* colLabelWin);
     void ProcessCornerLabelMouseEvent(wxMouseEvent& event);
 
+    void HandleColumnAutosize(int col, const wxMouseEvent& event);
+
     void DoColHeaderClick(int col);
 
     void DoStartResizeCol(int col);