MacViews: draw combobox arrow backgrounds

ui/views/style/platform_style.cc

 // 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.
 
 #include "ui/views/style/platform_style.h"
 
 #include "build/build_config.h"
 #include "ui/base/material_design/material_design_controller.h"
+#include "ui/views/background.h"
 #include "ui/views/controls/button/label_button.h"
 #include "ui/views/controls/button/label_button_border.h"
 #include "ui/views/controls/focusable_border.h"
 #include "ui/views/controls/scrollbar/native_scroll_bar.h"
 
 namespace views {
 
 #if !defined(OS_MACOSX)
+
 // static
 scoped_ptr<FocusableBorder> PlatformStyle::CreateComboboxBorder() {
   return make_scoped_ptr(new FocusableBorder());
 }
 
 // static
+scoped_ptr<Background> PlatformStyle::CreateComboboxBackground() {
+  return nullptr;
+}
+
+// static
 scoped_ptr<LabelButtonBorder> PlatformStyle::CreateLabelButtonBorder(
     Button::ButtonStyle style) {
   if (!ui::MaterialDesignController::IsModeMaterial() ||
       style != Button::STYLE_TEXTBUTTON) {
     return make_scoped_ptr(new LabelButtonAssetBorder(style));
   }
 
   scoped_ptr<LabelButtonBorder> border(new views::LabelButtonBorder());
   border->set_insets(views::LabelButtonAssetBorder::GetDefaultInsetsForStyle(
       Button::STYLE_TEXTBUTTON));
   return border;
 }
 
 // static
 scoped_ptr<ScrollBar> PlatformStyle::CreateScrollBar(bool is_horizontal) {
   return make_scoped_ptr(new NativeScrollBar(is_horizontal));
 }
 #endif
 
 #if !defined(OS_LINUX) || defined(OS_CHROMEOS)
 // static
 scoped_ptr<Border> PlatformStyle::CreateThemedLabelButtonBorder(
     LabelButton* button) {
   return button->CreateDefaultBorder();
 }
 #endif
 
 }  // namespace views