Change base::TickClock to a ref counted class.

ash/system/chromeos/session/logout_confirmation_controller_unittest.cc

Index: ash/system/chromeos/session/logout_confirmation_controller_unittest.cc
diff --git a/ash/system/chromeos/session/logout_confirmation_controller_unittest.cc b/ash/system/chromeos/session/logout_confirmation_controller_unittest.cc
index fb9d3791ad18af6c10bd660e3e6937111be144b9..c8f511cd214d175947954ac9db223b4b83d20a80 100644
--- a/ash/system/chromeos/session/logout_confirmation_controller_unittest.cc
+++ b/ash/system/chromeos/session/logout_confirmation_controller_unittest.cc
@@ -67,12 +67,12 @@ class MockTimeSingleThreadTaskRunner : public base::SingleThreadTaskRunner {
 class MockClock : public base::TickClock {
  public:
   explicit MockClock(scoped_refptr<MockTimeSingleThreadTaskRunner> task_runner);
-  virtual ~MockClock();
-
   // base::TickClock:
   virtual base::TimeTicks NowTicks() override;
 
  private:
+  virtual ~MockClock();
+
   scoped_refptr<MockTimeSingleThreadTaskRunner> task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(MockClock);