chromium/third_party/blink/web_tests/compositing/iframes/iframe-content-flipping.html

<!DOCTYPE html>

<html>
<head>
  <style type="text/css" media="screen">
    iframe {
        margin: 20px;
        height: 200px;
        width: 200px;
        border: 1px solid black;
    }
    
    .composited {
      will-change: transform;
    }
    
  </style>
  <script src="../../resources/run-after-layout-and-paint.js"></script>
  <script type="text/javascript" charset="utf-8">
    function doTest()
    {
      if (window.testRunner)
        testRunner.waitUntilDone();

      runAfterLayoutAndPaint(function() {
        document.getElementById('iframe').className = 'composited';
        if (window.testRunner)
          testRunner.notifyDone();
      });
    }
    
    window.addEventListener('load', doTest, false);
  </script>
</head>
<body>

    <!-- Test with already-composited iframe contents, and iframe itself composited. -->
    <!-- You should see a green square, no red. -->
    <iframe id="iframe" scrolling="no" src="resources/red-green-subframe.html"></iframe>
    
</body>
</html>