Mark PaymentDetails.error as experimental

third_party/WebKit/Source/modules/payments/PaymentDetails.idl

 // 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.
 
 // https://w3c.github.io/browser-payment-api/#paymentdetails-dictionary
 
 dictionary PaymentDetails {
     PaymentItem total;
     sequence<PaymentItem> displayItems;
     sequence<PaymentShippingOption> shippingOptions;
     sequence<PaymentDetailsModifier> modifiers;
-    DOMString error;
+    [RuntimeEnabled=PaymentDetailsError] DOMString error;
 };