Re-factor system tray code controlling launcher visibility

ash/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_SYSTEM_TRAY_TRAY_BACKGROUND_VIEW_H_
 #define ASH_SYSTEM_TRAY_TRAY_BACKGROUND_VIEW_H_
 
 #include "ash/ash_export.h"
 #include "ash/launcher/background_animator.h"
 #include "ash/system/tray/tray_views.h"
@@ skipping 72 matching lines @@
 
   // Sets |contents| as a child and sets its background to |background_|.
   void SetContents(views::View* contents);
 
   // Sets whether the tray paints a background. Default is true, but is set to
   // false if a window overlaps the shelf.
   void SetPaintsBackground(
       bool value,
       internal::BackgroundAnimator::ChangeType change_type);
 
+  // Convenience function to call same function in status_area_widget_.
+  void UpdateShouldShowLauncher();
+
   StatusAreaWidget* status_area_widget() {
     return status_area_widget_;
   }
   TrayContainer* tray_container() const { return tray_container_; }
   ShelfAlignment shelf_alignment() const { return shelf_alignment_; }
 
  private:
   friend class TrayLayerAnimationObserver;
 
   // Called from Initialize after all status area trays have been created.
@@ skipping 17 matching lines @@
   scoped_ptr<internal::TrayLayerAnimationObserver>
       layer_animation_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayBackgroundView);
 };
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_TRAY_TRAY_BACKGROUND_VIEW_H_