durable.html

<script>
function log(str) {
  document.getElementById("log").innerText += (str + "\n");
}

function checkPermission() {
  navigator.storage.persistentPermission().then(function (result) {
    log("Query result was " + result);
  },
  function (error) {
    log(error);
  });
}

function requestPermission() {
  navigator.storage.requestPersistent().then(function (result) {
    log("Request result was " + result);
  },
  function (error) {
    log(error);
  });
}

window.onload = function() {
  document.getElementById("someButton").onclick = requestPermission;
  document.getElementById("checkButton").onclick = checkPermission;
  if (!navigator.storage) {
    log("Can't find navigator.storage, maybe you aren't running with " +
    "--enable-experimental-web-platform-features (or " +
    "chrome://flags/#enable-experimental-web-platform-features) or your " +
    "version of chrome is too old. You need at least ~46.0.2486.")
  }
}
</script>
<button id="someButton">Request</button>
<button id="checkButton">Query</button>
<div id="log"></div>