Reuse NativeThemeAuraDark for cros tray.

ash/common/system/tray/tray_background_view.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 ASH_COMMON_SYSTEM_TRAY_TRAY_BACKGROUND_VIEW_H_
 #define ASH_COMMON_SYSTEM_TRAY_TRAY_BACKGROUND_VIEW_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
@@ skipping 59 matching lines @@
 
   // Called after the tray has been added to the widget containing it.
   virtual void Initialize();
 
   // Initializes animations for the bubble.
   static void InitializeBubbleAnimations(views::Widget* bubble_widget);
 
   // views::View:
   void SetVisible(bool visible) override;
   const char* GetClassName() const override;
+  const ui::NativeTheme* GetNativeTheme() const override;
   void ChildPreferredSizeChanged(views::View* child) override;
   void GetAccessibleState(ui::AXViewState* state) override;
   void AboutToRequestFocusFromTabTraversal(bool reverse) override;
 
   // ActionableView:
   bool PerformAction(const ui::Event& event) override;
   gfx::Rect GetFocusBounds() override;
   void OnGestureEvent(ui::GestureEvent* event) override;
 
   // Called whenever the shelf alignment changes.
@@ skipping 82 matching lines @@
 
   std::unique_ptr<TrayWidgetObserver> widget_observer_;
   std::unique_ptr<TrayEventFilter> tray_event_filter_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayBackgroundView);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_TRAY_TRAY_BACKGROUND_VIEW_H_