> Does this work in other browsers? N/A

Firefox won't reject on "close". 

Thank you for the report! Will fix.

Marcos, can you explain a bit more of what's wrong in Chrome's behavior? It appears that you got the promise returned by PaymentResponse.complete() to reject, but it's not clear what the user did to achieve this. Thank you!

Sorry, this is a more reduced test case:

```
const methods = [{ supportedMethods: ["basic-card"] }];
const details = {
  total: {
    label: "Total due",
    amount: { currency: "USD", value: "65.00" },
  },
};
async function doPaymentRequest() {
  const payResponse = await new PaymentRequest(methods, details).show();
  await payResponse.complete("fail");
}
doPaymentRequest();
```

So, now, to reproduce: 
 1. paste code, 
 2. hit "Pay" button.
 3. Enter CVV, hit "confirm".
 4. Hit "Close". 

> but it's not clear what the user did to achieve this.

Hitting the "close" causes the promise to reject. That shouldn't happen per spec. Hitting "close" should resolve with undefined and not reject. 

Should PaymentResponse.complete() promise ever reject in any circumstance?

Yes. If called twice or more, for instance:
https://www.w3.org/TR/payment-request/#complete()-method

But hitting esc or hitting close on the UI shouldn’t cause a rejection after complete() is called. 

Let me know if this is not clear from the spec.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/92296b66078c265fd8af1b56455e9c3fc6fcd800

commit 92296b66078c265fd8af1b56455e9c3fc6fcd800
Author: Rouslan Solomakhin <rouslan@chromium.org>
Date: Tue Sep 26 19:46:03 2017

[Payments] Do not reject PaymentResponse.complete() promise

Before this patch, when the user closes the PaymentRequest error message
that states "Transaction failed, please try again,"
PaymentResponse.complete() promise would be rejected. This is contrary
to the spec, which says the PaymentResponse.complete() promise should be
resolved when the user closes the UI.

Spec:
https://www.w3.org/TR/payment-request/#complete()-method

This patch changes the behavior of closing browser to resolve the
PaymentResponse.complete() promise instead.

After this patch, when the user closes the PaymentRequest error message
that states "Transaction failed, please try again,"
PaymentResponse.complete() promise is resolved with undefined.

Bug:  756298 
Test: CompleteTest.ResolveCompletePromiseOnUnknownError
Test: CompleteTest.ResolveCompletePromiseOnUserClosingUI
Test: https://w3c-test.org/payment-request/payment-response/complete-method-manual.https.html
Change-Id: If21b4b1c459432acf6f3156ddf26304f04f87918
Reviewed-on: https://chromium-review.googlesource.com/682794
Commit-Queue: Rouslan Solomakhin <rouslan@chromium.org>
Reviewed-by: Mathieu Perreault <mathp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504463}
[modify] https://crrev.com/92296b66078c265fd8af1b56455e9c3fc6fcd800/third_party/WebKit/Source/modules/payments/CompleteTest.cpp
[modify] https://crrev.com/92296b66078c265fd8af1b56455e9c3fc6fcd800/third_party/WebKit/Source/modules/payments/PaymentRequest.cpp