Convert //ash from scoped_ptr to std::unique_ptr

ash/system/web_notification/web_notification_tray.cc

Index: ash/system/web_notification/web_notification_tray.cc
diff --git a/ash/system/web_notification/web_notification_tray.cc b/ash/system/web_notification/web_notification_tray.cc
index a8b1139d65648ed8ec48f8edb1238cdbf245df26..66924528a6f7cc3a8a0f3f5d8de3ffe159ee6e7a 100644
--- a/ash/system/web_notification/web_notification_tray.cc
+++ b/ash/system/web_notification/web_notification_tray.cc
@@ -103,8 +103,8 @@ class WebNotificationBubbleWrapper {
   views::TrayBubbleView* bubble_view() const { return bubble_->bubble_view(); }
 
  private:
-  scoped_ptr<message_center::MessageBubbleBase> bubble_;
-  scoped_ptr<TrayBubbleWrapper> bubble_wrapper_;
+  std::unique_ptr<message_center::MessageBubbleBase> bubble_;
+  std::unique_ptr<TrayBubbleWrapper> bubble_wrapper_;
 
   DISALLOW_COPY_AND_ASSIGN(WebNotificationBubbleWrapper);
 };