chromium/third_party/blink/renderer/core/testing/data/frameserialization/picture.html

<html>
<head>
<meta charset="utf8">
<title>Test Picture Element</title>
</head>
<body>
<picture>
  <source media="(min-width: 500px)" srcset="2x.png">
  <source media="(min-width: 200px)" srcset="1x.png">
  <img />
</picture>
</body>
</html>