Codebase Browser
chromium
Go to App

chromium/third_party/blink/web_tests/plugins/resources/frame-with-plugin-subframe.html 

<!DOCTYPE html>

<html>
<body>
    <iframe src="missing-plugin-page.html"></iframe>
    <embed id="testPlugin" type="application/x-missing-plugin" width="200" height="200"></embed>
</body>
</html>