Edit in JSFiddle

var output = document.getElementById('output');

function runTest(useDeliver) {
  var obj = { foo: 'bar' };

  output.textContent = '';
 
  function handleChange(records) {
    output.textContent += '!CHANGE!\n';
  }
  
  Object.observe(obj, handleChange);
  
  output.textContent += 'BEGIN\n';
  
  obj.foo = 'baz';
  
  if (useDeliver) {
    Object.deliverChangeRecords(handleChange);
  }
  
  output.textContent += 'END\n';  
}
<button onclick="runTest(true)">With deliverChangeRecords</button>
<button onclick="runTest(false)">Without deliverChangeRecords</button>
<pre id="output"></pre>