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chromium/content/test/data/payments/payment_app_invocation.html 

<!doctype html>
<head>
<title>Payment App: Test for invoking payment app</title>
<script src="../result_queue.js"></script>
<script>
var resultQueue = new ResultQueue();
navigator.serviceWorker.addEventListener('message', e => {
  resultQueue.push(e.data);
});
</script>
</head>