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

ios/chrome/browser/payments/payment_request_unittest.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.h"
 
 #include "base/strings/utf_string_conversions.h"
 #include "components/autofill/core/browser/autofill_test_utils.h"
 #include "components/autofill/core/browser/test_personal_data_manager.h"
 #include "components/payments/core/currency_formatter.h"
@@ skipping 35 matching lines @@
   EXPECT_EQ(base::UTF8ToUTF16("55.00"), currency_formatter->Format("55.00"));
   EXPECT_EQ("USD", currency_formatter->formatted_currency_code());
 }
 
 // Tests that the accepted card networks are identified correctly.
 TEST(PaymentRequestTest, AcceptedPaymentNetworks) {
   web::PaymentRequest web_payment_request;
   autofill::TestPersonalDataManager personal_data_manager;
 
   payments::PaymentMethodData method_datum1;
-  method_datum1.supported_methods.push_back(base::ASCIIToUTF16("visa"));
+  method_datum1.supported_methods.push_back("visa");
   web_payment_request.method_data.push_back(method_datum1);
   payments::PaymentMethodData method_datum2;
-  method_datum2.supported_methods.push_back(base::ASCIIToUTF16("mastercard"));
+  method_datum2.supported_methods.push_back("mastercard");
   web_payment_request.method_data.push_back(method_datum2);
 
   PaymentRequest payment_request(web_payment_request, &personal_data_manager);
   ASSERT_EQ(2U, payment_request.supported_card_networks().size());
   EXPECT_EQ("visa", payment_request.supported_card_networks()[0]);
   EXPECT_EQ("mastercard", payment_request.supported_card_networks()[1]);
 }
 
 // Tests that credit cards can be added to the list of cached credit cards.
 TEST(PaymentRequestTest, AddCreditCard) {
   web::PaymentRequest web_payment_request;
   autofill::TestPersonalDataManager personal_data_manager;
 
   PaymentRequest payment_request(web_payment_request, &personal_data_manager);
   EXPECT_EQ(0U, payment_request.credit_cards().size());
 
   autofill::CreditCard credit_card = autofill::test::GetCreditCard();
   payment_request.AddCreditCard(credit_card);
   ASSERT_EQ(1U, payment_request.credit_cards().size());
   EXPECT_EQ(credit_card, *payment_request.credit_cards()[0]);
 }