Convert //ash from scoped_ptr to std::unique_ptr

ash/wm/overview/window_grid.h

Index: ash/wm/overview/window_grid.h
diff --git a/ash/wm/overview/window_grid.h b/ash/wm/overview/window_grid.h
index 2865be853b4a76168e364b0a302e401716ebbfab..49841725fc8954a4b5acda35648d596d64c6a9e2 100644
--- a/ash/wm/overview/window_grid.h
+++ b/ash/wm/overview/window_grid.h
@@ -7,12 +7,12 @@
 
 #include <stddef.h>
 
+#include <memory>
 #include <set>
 #include <vector>
 
 #include "ash/wm/overview/window_selector.h"
 #include "base/macros.h"
-#include "base/memory/scoped_ptr.h"
 #include "ui/aura/window_observer.h"
 
 namespace aura {
@@ -133,7 +133,7 @@ class ASH_EXPORT WindowGrid : public aura::WindowObserver {
   std::set<aura::Window*> observed_windows_;
 
   // Widget that indicates to the user which is the selected window.
-  scoped_ptr<views::Widget> selection_widget_;
+  std::unique_ptr<views::Widget> selection_widget_;
 
   // Current selected window position.
   size_t selected_index_;