[Payments] Add combobox support to editors.

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

Index: chrome/browser/ui/views/payments/validating_combobox.h
diff --git a/chrome/browser/ui/views/payments/validating_combobox.h b/chrome/browser/ui/views/payments/validating_combobox.h
new file mode 100644
index 0000000000000000000000000000000000000000..105759a10f3dffaf5d84db7620d2326f83e65f73
--- /dev/null
+++ b/chrome/browser/ui/views/payments/validating_combobox.h
@@ -0,0 +1,40 @@
+// 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_VALIDATING_COMBOBOX_H_
+#define CHROME_BROWSER_UI_VIEWS_PAYMENTS_VALIDATING_COMBOBOX_H_
+
+#include "base/macros.h"
+#include "chrome/browser/ui/views/payments/validation_delegate.h"
+#include "ui/views/controls/combobox/combobox.h"
+
+namespace payments {
+
+class ValidatingCombobox : public views::Combobox {
+ public:
+  ValidatingCombobox(std::unique_ptr<ui::ComboboxModel> model,
+                     std::unique_ptr<ValidationDelegate> delegate);
+  ~ValidatingCombobox() override;
+
+  // Combobox:
+  // The first validation will happen on blur.
+  void OnBlur() override;
+
+  // Called when the combobox contents is changed. May do validation.
+  void OnContentsChanged();
+
+ private:
+  // Will call to the ValidationDelegate to validate the contents of the
+  // combobox.
+  void Validate();
+
+  std::unique_ptr<ValidationDelegate> delegate_;
+  bool was_blurred_;
+
+  DISALLOW_COPY_AND_ASSIGN(ValidatingCombobox);
+};
+
+}  // namespace payments
+
+#endif  // CHROME_BROWSER_UI_VIEWS_PAYMENTS_VALIDATING_COMBOBOX_H_