Convert //ash from scoped_ptr to std::unique_ptr

ash/drag_drop/drag_image_view.h

Index: ash/drag_drop/drag_image_view.h
diff --git a/ash/drag_drop/drag_image_view.h b/ash/drag_drop/drag_image_view.h
index ee504f9abe62191f434f83e888fa529ca85f1a6a..8211c769d5faaead54d264e5dc5ffcae31053be0 100644
--- a/ash/drag_drop/drag_image_view.h
+++ b/ash/drag_drop/drag_image_view.h
@@ -5,6 +5,8 @@
 #ifndef ASH_DRAG_DROP_DRAG_IMAGE_VIEW_H_
 #define ASH_DRAG_DROP_DRAG_IMAGE_VIEW_H_
 
+#include <memory>
+
 #include "base/macros.h"
 #include "ui/base/dragdrop/drag_drop_types.h"
 #include "ui/views/controls/image_view.h"
@@ -71,7 +73,7 @@ class DragImageView : public views::ImageView {
   // Overridden from views::view
   void Layout() override;
 
-  scoped_ptr<views::Widget> widget_;
+  std::unique_ptr<views::Widget> widget_;
   gfx::Size widget_size_;
 
   ui::DragDropTypes::DragEventSource drag_event_source_;