Convert //ash from scoped_ptr to std::unique_ptr

ash/accelerators/exit_warning_handler.h

Index: ash/accelerators/exit_warning_handler.h
diff --git a/ash/accelerators/exit_warning_handler.h b/ash/accelerators/exit_warning_handler.h
index fb9d721af60245bf1a76c784f5f953d29a777d4f..aa17eab83064e55a580edb83e75fb1a06e95c25a 100644
--- a/ash/accelerators/exit_warning_handler.h
+++ b/ash/accelerators/exit_warning_handler.h
@@ -5,9 +5,10 @@
 #ifndef ASH_ACCELERATORS_EXIT_WARNING_HANDLER_H_
 #define ASH_ACCELERATORS_EXIT_WARNING_HANDLER_H_
 
+#include <memory>
+
 #include "ash/ash_export.h"
 #include "base/macros.h"
-#include "base/memory/scoped_ptr.h"
 #include "base/timer/timer.h"
 #include "ui/base/accelerators/accelerator.h"
 
@@ -73,7 +74,7 @@ class ASH_EXPORT ExitWarningHandler {
   void Hide();
 
   State state_;
-  scoped_ptr<views::Widget> widget_;
+  std::unique_ptr<views::Widget> widget_;
   base::OneShotTimer timer_;
 
   // Flag to suppress starting the timer for testing. For test we call