]);
        }
      }

      /**
       * Called at ready time with bag of instance properties that overwrote
       * accessors when the element upgraded.
       *
       * The default implementation sets these properties back into the
       * setter at ready time.  This method is provided as an override
       * point for customizing or providing more efficient initialization.
       *
       * @param {Object} props Bag of property values that were overwritten
       *   when creating property accessors.