Steps to reproduce the problem:
1. In DevTools on Chrome for Android and copy and paste the following code TWICE:

new PaymentRequest([{supportedMethods: ['visa']}], {
  total: {
    label: 'Example Total Label',
    amount: {
      currency: 'USD',
      value: '123',
    },
  },
}, {}).show();

What is the expected behavior?
The error should indicate that the PaymentRequest UI is currently open and cannot be re-opened.

What went wrong?
The error is simply "DOMException: Request cancelled".

Something along the lines of "DOMException: Payment request is currently open." would be more helpful for developers.

Did this work before? N/A 

Does this work in other browsers? N/A

Chrome version: 57.0.2987.133  Channel: stable
OS Version: 
Flash Version: