Codebase Browser
chromium
Go to App

chromium/content/test/data/https_upgrade_cross_site.html 

<!DOCTYPE html>
<html>
<title>Cross Site HTTPS upgrade</title>

<meta http-equiv="Content-Security-Policy" content="upgrade-insecure-requests">

<body>
  <iframe src="http://other.com/title1.html"></iframe>
</body>
</html>