[Payments] base::string16 -> std::string in PaymentMethodData

ios/chrome/browser/payments/payment_request_test_util.mm

 // Copyright 2017 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.
 
 #include "ios/chrome/browser/payments/payment_request_test_util.h"
 
 #include "base/strings/utf_string_conversions.h"
 #include "components/payments/core/payment_method_data.h"
 #include "ios/web/public/payments/payment_request.h"
 
 #if !defined(__has_feature) || !__has_feature(objc_arc)
 #error "This file requires ARC support."
 #endif
 
 namespace payment_request_test_util {
 
 web::PaymentRequest CreateTestWebPaymentRequest() {
   web::PaymentRequest web_payment_request;
   payments::PaymentMethodData method_datum;
-  method_datum.supported_methods.push_back(base::ASCIIToUTF16("visa"));
-  method_datum.supported_methods.push_back(base::ASCIIToUTF16("amex"));
+  method_datum.supported_methods.push_back("visa");
+  method_datum.supported_methods.push_back("amex");
   web_payment_request.method_data.push_back(method_datum);
   web_payment_request.details.total.label = base::ASCIIToUTF16("Total");
   web_payment_request.details.total.amount.value = base::ASCIIToUTF16("1.00");
   web_payment_request.details.total.amount.currency = base::ASCIIToUTF16("USD");
   web::PaymentItem display_item;
   display_item.label = base::ASCIIToUTF16("Subtotal");
   display_item.amount.value = base::ASCIIToUTF16("1.00");
   display_item.amount.currency = base::ASCIIToUTF16("USD");
   web_payment_request.details.display_items.push_back(display_item);
   web::PaymentShippingOption shipping_option;
   shipping_option.id = base::ASCIIToUTF16("123456");
   shipping_option.label = base::ASCIIToUTF16("1-Day");
   shipping_option.amount.value = base::ASCIIToUTF16("0.99");
   shipping_option.amount.currency = base::ASCIIToUTF16("USD");
   shipping_option.selected = true;
   web_payment_request.details.shipping_options.push_back(shipping_option);
   web::PaymentShippingOption shipping_option2;
   shipping_option2.id = base::ASCIIToUTF16("654321");
   shipping_option2.label = base::ASCIIToUTF16("10-Days");
   shipping_option2.amount.value = base::ASCIIToUTF16("0.01");
   shipping_option2.amount.currency = base::ASCIIToUTF16("USD");
   shipping_option2.selected = false;
   web_payment_request.details.shipping_options.push_back(shipping_option2);
   web_payment_request.options.request_shipping = true;
   return web_payment_request;
 }
 
 }  // namespace payment_request_test_util