[ash-md] Wired in the Shelf color to be derived from the Wallpaper.

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 108 matching lines @@
 
   TrayContainer* tray_container() const { return tray_container_; }
   ShelfAlignment shelf_alignment() const { return shelf_alignment_; }
   TrayEventFilter* tray_event_filter() { return tray_event_filter_.get(); }
   WmShelf* shelf() { return wm_shelf_; }
 
   // Updates the arrow visibility based on the launcher visibility.
   void UpdateBubbleViewArrow(views::TrayBubbleView* bubble_view);
 
   // ShelfBackgroundAnimatorObserver:
-  void UpdateShelfItemBackground(int alpha) override;
+  void UpdateShelfItemBackground(SkColor color) override;
 
   // Updates the visibility of this tray's separator.
   void set_separator_visibility(bool visible) { separator_visible_ = visible; }
 
   // Gets the anchor for bubbles, which is tray_container().
   views::View* GetBubbleAnchor() const;
 
   // Gets additional insets for positioning bubbles relative to
   // tray_container().
   gfx::Insets GetBubbleAnchorInsets() const;
@@ skipping 48 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_