Codebase Browser
chromium
Go to App

chromium/chrome/test/data/client_hints/frame_3p_ot.html 

<html>
<head>
<link rel="stylesheet" href="https://my-site-a.com:44444/style.css">
</head>
<body>
<iframe src="https://my-site-b.com:44444/basic.html"></iframe>
</body>
</html>