code: function _restoreOverriddenDefault(name, state) {
          if (state.overridden[name]) {
              var language = getLanguage(state.overridden[name]);
              language[state.add](name);
              delete state.overridden[name];
          }
      }
docs: @private
  
  If a default file extension or name was overridden by a pref, restore it.
  
  @param {string} name Extension or filename that should be restored
  @param {{overridden: string, add: string}} prefState object for the pref that is currently being updated