tsFixtured = false;

      this.forcePolyfillAttachedStateSynchrony();
    },

    forcePolyfillAttachedStateSynchrony: function () {
      // Force synchrony in attachedCallback and detachedCallback where
      // implemented, in the event that we are dealing with one of these async
      // polyfills:
      // 1. Web Components CustomElements polyfill (v1 or v0).
      if (window.customElements && window.customElements.flush) {
        window.customElements.flush();
      } else if (window.CustomElements 