[Payments] Add combobox support to editors.

chrome/browser/ui/views/payments/preselected_combobox_model.cc

Index: chrome/browser/ui/views/payments/preselected_combobox_model.cc
diff --git a/chrome/browser/ui/views/payments/preselected_combobox_model.cc b/chrome/browser/ui/views/payments/preselected_combobox_model.cc
new file mode 100644
index 0000000000000000000000000000000000000000..14339d980df14f084311a665b8fb409cd738818a
--- /dev/null
+++ b/chrome/browser/ui/views/payments/preselected_combobox_model.cc
@@ -0,0 +1,20 @@
+// 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.
+
+#include "chrome/browser/ui/views/payments/preselected_combobox_model.h"
+
+namespace payments {
+
+PreselectedComboboxModel::PreselectedComboboxModel(
+    const std::vector<base::string16>& items,
+    int default_index)
+    : SimpleComboboxModel(items), default_index_(default_index) {}
+
+PreselectedComboboxModel::~PreselectedComboboxModel() {}
+
+int PreselectedComboboxModel::GetDefaultIndex() const {
+  return default_index_;
+}
+
+}  // namespace payments