Codebase Browser
chromium
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chromium/third_party/blink/web_tests/http/tests/devtools/tracing/resources/timeline-iframe-paint.html 

<html>
<head>
<body style="margin: 0">
    <div style="display: block; position: absolute; left: 15px; top: 15px; width: 20px; height: 20px; background-color: blue"></div>
</body>
</html>