[Payments] Currency formatter for order amounts.

components/payments/currency_formatter.h

Index: components/payments/currency_formatter.h
diff --git a/components/payments/currency_formatter.h b/components/payments/currency_formatter.h
new file mode 100644
index 0000000000000000000000000000000000000000..54d1906b5feb3ddd3183058b240c6131907c1d87
--- /dev/null
+++ b/components/payments/currency_formatter.h
@@ -0,0 +1,28 @@
+// 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.
+
+#ifndef COMPONENTS_PAYMENTS_CURRENCY_FORMATTER_H_
+#define COMPONENTS_PAYMENTS_CURRENCY_FORMATTER_H_
+
+#include <string>
+
+#include "third_party/icu/source/common/unicode/locid.h"
+
+namespace payments {
+
+// Formats the |amount| according to the |currency_code|, which typically
+// adheres to [ISO4217] (for example, "USD" for US Dollars). The result will NOT
+// contain the currency code, nor a subset of it. Rather, the caller of this
+// function should display the currency code separately. Note that |amount|
+// and |currency_code| should have been validated (as part of
+// payment_details_validation.h) before this is called, but this function will
+// still do light validation, and return |amount| in failure cases. The return
+// value may contain non-breaking space.
+const std::string FormatAmountForCurrency(const std::string& amount,

[please use gerrit instead, 2017/01/11 18:29:30]

The "const" keyword here does not seem to server any purpose?

[Mathieu, 2017/01/11 22:22:26]

Done.

+                                          const std::string& currency_code,
+                                          const icu::Locale& locale);
+
+}  // namespace payments
+
+#endif  // COMPONENTS_PAYMENTS_CURRENCY_FORMATTER_H_