<!doctype html>
<html>
<head>
  <style>
    html, body {
      height: 100%;
    }
    
    .container {
      height: 100%;
      overflow: scroll;
    }
    iframe {
      display: block;
      width: 200px;
      height: 600px;
    }
  </style>
</head>
<body>
  <div class="container">
    <iframe src="data:text/html,Scroll this out of the view."></iframe>
    <iframe src="data:text/html,Stop here and inspect if layouts got initiated, while scolling in the Web Inspector."></iframe>
  </div>
</body>
</html>