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chromium
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chromium/chrome/test/data/client_hints/accept_ch_ua_cross_origin_iframe_with_ot_request.html 

<html>
<link rel="icon" href="data:;base64,=">
<body>
<iframe src="https://my-site.com:44444/simple_3p_ot.html"></iframe>
</body>
</html>