chromium/chrome/test/data/devtools/pause_when_loading_devtools.html

<html>
<head>
<script>

// Try to call debugger in loop so that pause event happens
// during DevTools frontend load.
function callDebugger() {
  debugger;
  setTimeout(callDebugger, 0);
}

</script>
</head>
<body onload='callDebugger()'>
Call debugger repeatedly.
</body>
</html>