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chromium/third_party/blink/web_tests/external/wpt/cookies/schemeful-same-site/resources/navigateToInsecurePostToParent.html 

<!DOCTYPE html>
<meta charset="utf-8">
<script src="/cookies/resources/cookie-helper.sub.js"></script>
<script>
      window.location = INSECURE_ORIGIN + "/cookies/resources/postToParent.py";
</script>