ting = false;
      // with-backdrop needs tabindex to be set in order to trap the focus.
      // If it is not set, IronOverlayBehavior will set it, and remove it if with-backdrop = false.
      this.__shouldRemoveTabIndex = false;
      // Used for wrapping the focus on TAB / Shift+TAB.
      this.__firstFocusableNode = this.__lastFocusableNode = null;
      // Used for requestAnimationFrame when opened changes.
      this.__openChangedAsync = null;
      // Used for requestAnimationFrame when iron-resize