code: function (widgetName, includeLoaded) {
              var classpath = this.widgets[widgetName];
              if (classpath == null) {
                  return null;
              }
              if (includeLoaded || Aria.getClassRef(classpath) == null) {
                  return [classpath];
              }
              return [];
          }
docs: Return a list of dependencies which must be loaded before a widget can be used.
  @param {String} widgetName the name of the widget - e.g. TextField
  @param {Boolean} includeLoaded [optional, default: false] if true, also include dependencies which are
  already loaded
  @return {Array} array of classpaths which should be loaded so that the widget can be used. Must return null
  if the widget does not exist. Return an empty array if the widget is already usable and includeLoaded is
  false.