Send the autosize column event for grid native header columns

Send wxEVT_GRID_COL_AUTO_SIZE on double clicking on a separator line of
the grid native header to allow override default behaviour.

include/wx/generic/private/grid.h

@@ -191,11 +191,9 @@ private:
     }
 
     // override to implement column auto sizing
-    virtual bool UpdateColumnWidthToFit(unsigned int idx, int widthTitle) wxOVERRIDE
+    virtual bool UpdateColumnWidthToFit(unsigned int idx, int WXUNUSED(widthTitle)) wxOVERRIDE
     {
-        // TODO: currently grid doesn't support computing the column best width
-        //       from its contents so we just use the best label width as is
-        GetOwner()->SetColSize(idx, widthTitle);
+        GetOwner()->HandleColumnAutosize(idx, GetDummyMouseEvent());
 
         return true;
     }