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chromium/third_party/blink/web_tests/external/wpt/partitioned-popins/resources/partitioned-popins.cookies-iframe.html 

<!doctype html>
<meta charset="utf-8">
<script src="/resources/testdriver.js"></script>
<script src="/resources/testdriver-vendor.js"></script>
<script>
(async function() {
  test_driver.set_test_context(window.top);

  // Step 5 (partitioned-popins/partitioned-popins.cookies.tentative.sub.https.window.js)
  const id = (new URLSearchParams(window.location.search)).get("id");
  document.cookie = "third-party-strict=" + id + "; Partitioned; SameSite=Strict; Secure";
  document.cookie = "third-party-lax=" + id + "; Partitioned; SameSite=Lax; Secure";
  document.cookie = "third-party-none=" + id + "; Partitioned; SameSite=None; Secure";
  window.top.postMessage({type: "iframe-set", message: "Set third-party data"}, "*");
})();
</script>