PaymentRequest.abort() should return a promise.

third_party/WebKit/public/platform/modules/payments/payment_request.mojom

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 [JavaPackage="org.chromium.mojom.payments"]
 module blink.mojom;
 
 // The shipping address that the browser process provides to the renderer
 // process. Built either by the browser or a payment app.
 struct PaymentAddress {
@@ skipping 50 matching lines @@
   PaymentAddress? shipping_address;
   string? shipping_option_id;
 };
 
 interface PaymentRequestClient {
   OnShippingAddressChange(PaymentAddress address);
   OnShippingOptionChange(string shipping_option_id);
   OnPaymentResponse(PaymentResponse response);
   OnError();
   OnComplete();
+  OnAbort(bool aborted_successfully);
 };
 
 struct PaymentItem {
   string label;
   CurrencyAmount amount;
 };
 
 struct ShippingOption {
   string id;
   string label;
@@ skipping 27 matching lines @@
 
 interface PaymentRequest {
   SetClient(PaymentRequestClient client);
   Show(array<PaymentMethodData> methodData,
        PaymentDetails details,
        PaymentOptions options);
   UpdateWith(PaymentDetails details);
   Abort();
   Complete(bool success);
 };