MacViews: draw combobox arrow backgrounds

ui/views/examples/combobox_example.h

 // Copyright (c) 2012 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 UI_VIEWS_EXAMPLES_COMBOBOX_EXAMPLE_H_
 #define UI_VIEWS_EXAMPLES_COMBOBOX_EXAMPLE_H_
 
 #include "base/macros.h"
 #include "ui/base/models/combobox_model.h"
 #include "ui/views/controls/combobox/combobox_listener.h"
@@ skipping 24 matching lines @@
 
   // ExampleBase:
   void CreateExampleView(View* container) override;
 
  private:
   // ComboboxListener:
   void OnPerformAction(Combobox* combobox) override;
 
   ComboboxModelExample combobox_model_;
   Combobox* combobox_ = nullptr;
+  Combobox* disabled_combobox_ = nullptr;
   Combobox* action_combobox_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(ComboboxExample);
 };
 
 }  // namespace examples
 }  // namespace views
 
 #endif  // UI_VIEWS_EXAMPLES_COMBOBOX_EXAMPLE_H_