Codebase Browser
chromium
Go to App

chromium/third_party/blink/web_tests/http/tests/devtools/layers/resources/composited-iframe.html 

<html>
<body>
<div id="subframe1" style="left: 20px; top: 20px; width: 80px; height: 80px; transform: translateZ(20px);"></div>
</body>
</html>