code: function makeRequestCallFromMutationObserver(callback) {
      var toggle = 1;
      var observer = new BrowserMutationObserver(callback);
      var node = document.createTextNode("");
      observer.observe(node, {characterData: true});
      return function requestCall() {
          toggle = -toggle;
          node.data = toggle;
      };
  }
docs: To request a high priority event, we induce a mutation observer by toggling the text of a text node between "1" and "-1".