Change base::TickClock to a ref counted class.

ash/system/chromeos/session/logout_confirmation_controller.cc

Index: ash/system/chromeos/session/logout_confirmation_controller.cc
diff --git a/ash/system/chromeos/session/logout_confirmation_controller.cc b/ash/system/chromeos/session/logout_confirmation_controller.cc
index fdf1cc627c751d59bb5b55777ddcc57463fb2b8a..aa41a24704e41636ff7c07c8b3e7eddeeaad3094 100644
--- a/ash/system/chromeos/session/logout_confirmation_controller.cc
+++ b/ash/system/chromeos/session/logout_confirmation_controller.cc
@@ -55,8 +55,8 @@ void LogoutConfirmationController::ConfirmLogout(
 }
 
 void LogoutConfirmationController::SetClockForTesting(
-    scoped_ptr<base::TickClock> clock) {
-  clock_ = clock.Pass();
+    scoped_refptr<base::TickClock> clock) {
+  clock_.swap(clock);
 }
 
 void LogoutConfirmationController::OnLockStateChanged(bool locked) {