chromium/content/test/data/frame_tree/page_with_transformed_iframe.html

<!DOCTYPE html>
<html>
  <head>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <style>
    iframe {
      position: absolute;
      top: 100px;
      left: 100px;
      width: 100px;
      height: 100px;
      transform: rotateZ(45deg);
      transform-origin: top left;
      border: none;
    }
    </style>
  </head>
  <body>
    <iframe src="/cross-site/baz.com/title1.html"></iframe>
  </body>
</html>