Change base::TickClock to a ref counted class.

ui/display/chromeos/x11/native_display_event_dispatcher_x11.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/time/default_tick_clock.h"
 #include "ui/display/chromeos/x11/native_display_event_dispatcher_x11.h"
 #include "ui/display/chromeos/x11/display_mode_x11.h"
 #include "ui/display/chromeos/x11/display_snapshot_x11.h"
 #include "ui/events/platform/platform_event_source.h"
 
@@ skipping 81 matching lines @@
       return ui::POST_DISPATCH_PERFORM_DEFAULT;
     }
   }
 
   delegate_->NotifyDisplayObservers();
 
   return ui::POST_DISPATCH_PERFORM_DEFAULT;
 }
 
 void NativeDisplayEventDispatcherX11::SetTickClockForTest(
-    scoped_ptr<base::TickClock> tick_clock) {
-  tick_clock_ = tick_clock.Pass();
+    const scoped_refptr<base::TickClock>& tick_clock) {
+  tick_clock_ = tick_clock;
   startup_time_ = tick_clock_->NowTicks();
 }
 
 }  // namespace ui