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chromium/chrome/test/data/extensions/api_test/service_worker/registration/ntp_extension/extension_version_1/ntp.html 

<!doctype html>
<html>
  <head>
    <title>Custom NTP test v1</title>
    <script src="ntp.js"></script>
  </head>
  <body>
    This is a test custom NTP page.
  </body>
</html>