 is fired.
      this.__onIronResizeAsync = null;
      this._ensureSetup();
    },

    attached: function() {
      // Call _openedChanged here so that position can be computed correctly.
      if (this.opened) {
        this._openedChanged();
      }
      this._observer = Polymer.dom(this).observeNodes(this._onNodesChange);
    },

    detached: function() {
      Polymer.dom(this).unobserveNodes(this._observer);
      this._observer = null;
      this.opened = false;
      if (this.withBackdrop) {
    