Function waitForMutationObserver

test/unit/test-3p-environment.js:208–219

(iframe)

  }

  function waitForMutationObserver(iframe) {
    if (
      iframe.contentWindow &&
      iframe.contentWindow.document &&
      iframe.contentWindow.document.body.childNodes.length
    ) {
      return timer.promise(10);
    }
    return loadPromise(iframe).then(() => {
      return timer.promise(10);
    });
  }

  function makeChildIframeSrcdoc(win) {
    const doc = win.document;