[PaymentReqeust] Add error message in PaymentDetails. (in blink side)

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.payments.mojom"]
 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 85 matching lines @@
   array<string> supported_methods;
   PaymentItem total;
   array<PaymentItem> additional_display_items;
 };
 
 struct PaymentDetails {
   PaymentItem total;
   array<PaymentItem> display_items;
   array<PaymentShippingOption> shipping_options;
   array<PaymentDetailsModifier> modifiers;
+  string error;
 };
 
 struct PaymentOptions {
   bool request_payer_name;
   bool request_payer_email;
   bool request_payer_phone;
   bool request_shipping;
 };
 
 struct PaymentMethodData {
@@ skipping 19 matching lines @@
 interface PaymentRequest {
   Init(PaymentRequestClient client,
        array<PaymentMethodData> methodData,
        PaymentDetails details,
        PaymentOptions options);
   Show();
   UpdateWith(PaymentDetails details);
   Abort();
   Complete(PaymentComplete result);
 };