PaymentRequest: The currencySystem should be non-nullable.

components/payments/payment_request.h

 // 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.
 
 #ifndef COMPONENTS_PAYMENTS_PAYMENT_REQUEST_H_
 #define COMPONENTS_PAYMENTS_PAYMENT_REQUEST_H_
 
 #include <memory>
 #include <string>
 #include <vector>
@@ skipping 38 matching lines @@
 
   void Cancel();
   void OnError();
 
   // Returns the CurrencyFormatter instance for this PaymentRequest.
   // |locale_name| should be the result of the browser's GetApplicationLocale().
   // Note: Having multiple currencies per PaymentRequest is not supported; hence
   // the CurrencyFormatter is cached here.
   CurrencyFormatter* GetOrCreateCurrencyFormatter(
       const std::string& currency_code,
-      const base::Optional<std::string> currency_system,
+      const std::string& currency_system,
       const std::string& locale_name);
 
   // Returns the Autofill Profile, representing the shipping address and contact
   // information, currently selected for this PaymentRequest flow. If
   // unpopulated, populates with and returns the 0th profile on record for this
   // user, if it exists; or nullptr otherwise. Profile is owned by the request
   // object, not the caller.
   autofill::AutofillProfile* GetCurrentlySelectedProfile();
 
   // Returns the currently selected credit card for this PaymentRequest flow.
@@ skipping 14 matching lines @@
   payments::mojom::PaymentDetailsPtr details_;
   std::unique_ptr<CurrencyFormatter> currency_formatter_;
   std::unique_ptr<autofill::AutofillProfile> profile_;
 
   DISALLOW_COPY_AND_ASSIGN(PaymentRequest);
 };
 
 }  // namespace payments
 
 #endif  // COMPONENTS_PAYMENTS_PAYMENT_REQUEST_H_