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

ios/chrome/browser/payments/payment_request_test_util.mm

Index: ios/chrome/browser/payments/payment_request_test_util.mm
diff --git a/ios/chrome/browser/payments/payment_request_test_util.mm b/ios/chrome/browser/payments/payment_request_test_util.mm
index 7fd7032394c5ad400cd9793fee843ba8b2981edb..706ec3e0893b4570b63d596628ae77192682bafb 100644
--- a/ios/chrome/browser/payments/payment_request_test_util.mm
+++ b/ios/chrome/browser/payments/payment_request_test_util.mm
@@ -17,8 +17,8 @@ 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");