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chromium/third_party/blink/web_tests/http/tests/inspector-protocol/prerender/resources/prerender-echo-header.html 

<!doctype html>
<html>
<!-- Start a prerender. -->
<script type="speculationrules">
{
  "prerender": [{
    "source": "list",
    "urls": ["echo-headers-and-broadcast.php"]
  }]
}
</script>
<body><a href="echo-headers-and-broadcast.php" id="link">link</a></body>
</html>