Steps to reproduce the problem:
Run the following code in DevTools Console:

const supportedCreditCards = {
    supportedMethods: ['basic-card'],
  };
  const supportedPaymentMethods = [supportedCreditCards];

  const transactionDetails = {
    total: {
      label: 'Total',
      amount: {
        currency: 'USD',
        value: '0',
      },
    },
  };

  const options = {};

  const paymentRequest = new PaymentRequest(
    supportedPaymentMethods, transactionDetails, options);
  paymentRequest.show()
  .then((paymentResponse) => {
    return new Promise((resolve) => {
      // NOOP. Never resolve the promise.
    });
  })
  .catch((err) => {
    console.error('PaymentRequest error: ', err);
  });

What is the expected behavior?
An error to be logged when the PaymentRequest UI timesout.

What went wrong?
The UI closes and a user error is shown, but nothing indicates to developers that it was a timeout that causes the closing of the UI.

Did this work before? N/A 

Does this work in other browsers? N/A

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