[Payments] Add combobox support to editors.

chrome/browser/ui/views/payments/validation_delegate.h

+// 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 CHROME_BROWSER_UI_VIEWS_PAYMENTS_VALIDATION_DELEGATE_H_
+#define CHROME_BROWSER_UI_VIEWS_PAYMENTS_VALIDATION_DELEGATE_H_
+
+namespace views {
+class Combobox;
+class Textfield;
+}  // namespace views
+
+namespace payments {
+
+class ValidationDelegate {
+ public:
+  virtual ~ValidationDelegate() {}
+
+  // Only the delegate knows how to validate the textfield.
+  virtual bool ValidateTextfield(views::Textfield* textfield) = 0;
+
+  virtual bool ValidateCombobox(views::Combobox* combobox) = 0;
+};
+
+}  // namespace payments
+
+#endif  // CHROME_BROWSER_UI_VIEWS_PAYMENTS_VALIDATION_DELEGATE_H_