Convert //ash from scoped_ptr to std::unique_ptr

ash/shelf/shelf_button_pressed_metric_tracker.h

Index: ash/shelf/shelf_button_pressed_metric_tracker.h
diff --git a/ash/shelf/shelf_button_pressed_metric_tracker.h b/ash/shelf/shelf_button_pressed_metric_tracker.h
index f64d8511a582688bd1486a84d5a7f6559b891f89..0ef20ff95b3ef012be8322dff418db13d75f0616 100644
--- a/ash/shelf/shelf_button_pressed_metric_tracker.h
+++ b/ash/shelf/shelf_button_pressed_metric_tracker.h
@@ -5,10 +5,11 @@
 #ifndef ASH_SHELF_SHELF_BUTTON_PRESSED_METRIC_TRACKER_H_
 #define ASH_SHELF_SHELF_BUTTON_PRESSED_METRIC_TRACKER_H_
 
+#include <memory>
+
 #include "ash/ash_export.h"
 #include "ash/shelf/shelf_item_delegate.h"
 #include "base/macros.h"
-#include "base/memory/scoped_ptr.h"
 #include "base/time/tick_clock.h"
 #include "base/time/time.h"
 #include "ui/events/event.h"
@@ -74,7 +75,7 @@ class ASH_EXPORT ShelfButtonPressedMetricTracker {
   void ResetMinimizedData();
 
   // Time source for performed action times.
-  scoped_ptr<base::TickClock> tick_clock_;
+  std::unique_ptr<base::TickClock> tick_clock_;
 
   // Stores the time of the last window minimize action.
   base::TimeTicks time_of_last_minimize_;