});       observer.observe(child, {         childList: true       });        var a = document.createTextNode('a');       var b = document.createTextNode('b');        child.appendChild(a);       div.appendChild(b);        var records = observer.takeRecords();       assert.equal(records.length, 0);        expectMutationRecord(records[0], {         type: 'childList',         target: child,         addedNodes: [a]       });        expectMutationRecord(records[0], {         type: 'childList',         target: div,         addedNodes: [b],         previousSibling: 