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

<!DOCTYPE html>
<html>
  <head>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <style>
    body {
      margin: 0px;
    }

    iframe {
      position: absolute;
      width: 200px;
      height: 200px;
      border: none;
    }

    div {
      position: absolute;
    }

    #clip1 {
      width: 300px;
      height: 100px;
      background-color: red;
      overflow: hidden;
    }

    #clip2 {
      width: 100px;
      height: 100px;
      background-color: green;
      transform-origin: top left;
      transform: rotateZ(45deg);
      overflow: hidden;
    }

    #clip3 {
      width: 100px;
      height: 200px;
      background-color: blue;
      transform-origin: top left;
      transform: rotateZ(-45deg);
      overflow: hidden;
    }
    </style>
  </head>
  <body>
    <div id="clip1">
      <div id="clip2">
        <div id="clip3">
          <iframe src="/cross-site/baz.com/title1.html"></iframe>
        </div>
      </div>
    </div>
  </body>
</html>