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chromium/chrome/test/data/extensions/platform_apps/window_controls/buttons/index.html 

<html lang="en-US" dir="ltr">
<head>
  <meta content="text/html; charset=UTF-8" http-equiv="Content-Type">
  <title>Test</title>
</head>
<body>
  <window-controls></window-controls>
</body>
</html>