chromium/chrome/test/data/page_load_metrics/document_with_duplicate_css.html

<html>
  <head>
    <link rel="stylesheet" type="text/css" href="background_image.css">
    <link rel="stylesheet" type="text/css" href="background_image.css">
  </head>
  <body>
   The page loads the same css file.
  </body>
</html>