title: PaymentRequest API not defined
body: <p>I am trying to run an example of the Payment request API as shown on <a href="https://www.youtube.com/watch?v=yelPlCVZLEE" rel="nofollow">https://www.youtube.com/watch?v=yelPlCVZLEE</a> .
  I have followed the process as they describe and i Have also run the following code:</p>
  
  <pre><code>function go() {
     console.log('Pay');
     var request = new PaymentRequest([{
              supportedMethods:['urn:payment:visa','urn:payment:mc','urn:payment:amex']
           }],
           {
              total: {
              label: "Total due",
              amount: { currencyCode: "USD", value: "60.00" }, // US$60.00
           }
       }
     );
  
  request.show()
    .then(function(response) {
      // process transaction response here
      return response.complete(true);
    })
    .then(function() {
      alert("Buy!");
    })
    .catch(function(e) {
      alert(e.name);
    });
   }
  </code></pre>
  
  <p>and I get the following error: Uncaught ReferenceError: PaymentRequest is not defined.</p>
  
  <p>If I run the test from : 
  <a href="http://github.adrianba.net/paymentrequest-demo/tests/payment-tests.html" rel="nofollow">http://github.adrianba.net/paymentrequest-demo/tests/payment-tests.html</a>
  It's says it's defined.
  What I am doing wrong?</p>