Convert //ash from scoped_ptr to std::unique_ptr

ash/system/tray/tray_background_view.h

Index: ash/system/tray/tray_background_view.h
diff --git a/ash/system/tray/tray_background_view.h b/ash/system/tray/tray_background_view.h
index ef391348c1a407684e659eabbfb30b4320fec61d..df447a5fb38370cd156919e65b88573bfc696ed6 100644
--- a/ash/system/tray/tray_background_view.h
+++ b/ash/system/tray/tray_background_view.h
@@ -5,6 +5,8 @@
 #ifndef ASH_SYSTEM_TRAY_TRAY_BACKGROUND_VIEW_H_
 #define ASH_SYSTEM_TRAY_TRAY_BACKGROUND_VIEW_H_
 
+#include <memory>
+
 #include "ash/ash_export.h"
 #include "ash/shelf/background_animator.h"
 #include "ash/shelf/shelf_types.h"
@@ -188,8 +190,8 @@ class ASH_EXPORT TrayBackgroundView : public ActionableView,
   // differently if set to true.
   bool draw_background_as_active_;
 
-  scoped_ptr<TrayWidgetObserver> widget_observer_;
-  scoped_ptr<TrayEventFilter> tray_event_filter_;
+  std::unique_ptr<TrayWidgetObserver> widget_observer_;
+  std::unique_ptr<TrayEventFilter> tray_event_filter_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayBackgroundView);
 };