chromium/chrome/test/data/iframe_rotated.html

<!DOCTYPE html>
<html>
  <style>
    iframe {
      position: absolute;
      left: 100px;
      top: 100px;
      width: 100px;
      height: 100px;
      transform: rotate(45deg);
      /* Removing external factor that might affect pixel accuracy */
      border: none;
      padding: 0;
      margin: 0;
    }
  </style>
  <iframe src="title1.html">
  </iframe>
</html>