MacViews: draw combobox arrow backgrounds

ui/views/style/platform_style.h

 // Copyright 2015 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_STYLE_PLATFORM_STYLE_H_
 #define UI_VIEWS_STYLE_PLATFORM_STYLE_H_
 
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "ui/views/controls/button/button.h"
 
 namespace views {
 
 class Border;
 class FocusableBorder;
 class LabelButton;
 class LabelButtonBorder;
 class ScrollBar;
 
 // Cross-platform API for providing platform-specific styling for toolkit-views.
 class PlatformStyle {
  public:
   // Creates the appropriate border for a focusable Combobox.
   static scoped_ptr<FocusableBorder> CreateComboboxBorder();
 
+  // Creates the appropriate background for a Combobox.
+  static scoped_ptr<Background> CreateComboboxBackground();
+
   // Creates the default label button border for the given |style|. Used when a
   // custom default border is not provided for a particular LabelButton class.
   static scoped_ptr<LabelButtonBorder> CreateLabelButtonBorder(
       Button::ButtonStyle style);
 
   // Applies the current system theme to the default border created by |button|.
   static scoped_ptr<Border> CreateThemedLabelButtonBorder(LabelButton* button);
 
   // Creates the default scrollbar for the given orientation.
   static scoped_ptr<ScrollBar> CreateScrollBar(bool is_horizontal);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PlatformStyle);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_STYLE_PLATFORM_STYLE_H_