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chromium/third_party/blink/web_tests/external/wpt/webmessaging/broadcastchannel/resources/sandboxed.html 

<!DOCTYPE html>
<meta charset=utf-8>
<script>
try {
  let c = new BroadcastChannel('foo');
  parent.postMessage('Created', '*');
} catch (e) {
  parent.postMessage('Exception: ' + e.name, '*');
}
</script>