partitioned-estimate-usage-details-service-workers-helper-frame.html

<!DOCTYPE html>
<meta name=help href="https://privacycg.github.io/storage-partitioning/">
<title>Helper frame</title>

<script>
  const usageDetails = async () => {
    return (await navigator.storage.estimate())
      .usageDetails.serviceWorkerRegistrations || 0
  }

  let details = {};

  window.addEventListener("message", async event => {
    if (event.data === "get-details") {
      details.source = "same-site";
      details.init = await usageDetails();
      event.source.postMessage(details, event.source.origin);
    }
  });

  window.addEventListener("load", async () => {
    if (parent.opener) {
      details.source = "cross-site";
      details.init = await usageDetails();
      parent.opener.postMessage(details, parent.opener.origin);
    }
  });

  window.parent.postMessage("iframe-is-ready", window.parent.origin);
</script>

chromium/third_party/blink/web_tests/external/wpt/storage/resources/partitioned-estimate-usage-details-service-workers-helper-frame.html