code: def GetLoadingOrder(self):
      
      result = {}
      for filename, mapping in self._file_mapping.iteritems():
        loading_order = mapping['loading_order']
        if loading_order is not None:
          result[loading_order] = filename
      return list(result[key] for key in sorted(result))
docs: Returns a list of filenames sorted by loading order.
      Only includes files that Loader's standardized loading knows how to load