Codebase Browser
chromium
Go to App

chromium/third_party/blink/web_tests/wpt_internal/cookies/resources/window.html 

<!doctype html>
<meta charset="utf-8">
<script>
// Step 3 (wpt_internal/cookies/dt-coexist.{}.sub.https.window.js)
document.cookie = "test=test;Secure;SameSite=None";
window.localStorage.setItem("test", "test");

// Step 4 (wpt_internal/cookies/dt-coexist.{}.sub.https.window.js)
window.opener.postMessage({type: "SetData"}, "*");
</script>