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chromium
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chromium/third_party/blink/web_tests/external/wpt/content-security-policy/navigate-to/support/spv-test-iframe3.sub.html 

<!DOCTYPE html>
<head>
  <script>
    window.addEventListener('securitypolicyviolation', function(e) {
      top.postMessage({iframe: 'iframe3', violatedDirective: e.violatedDirective}, '*');
    });
  </script>
</head>

<body>
  IFRAME 3
</body>