chromium/third_party/blink/web_tests/fast/frames/frame-set-scaling-centered.html

<html style="background-color: red; transform:  scale(0.5, 0.5);"><head><title>Frame Scale Test</title></head>
  <frameset style="border: 5px solid green;" cols="30%,*">
    <frame src="data:text/html,<body bgcolor='green'></body>">
    <frame src="data:text/html,<body bgcolor='green'></body>">
  </frameset>
</html>