Added the Ash.Tab.TimeBetweenSwitchToExistingTabUserActions histogram to track time between tab swit

ash/metrics/user_metrics_recorder.h

 // Copyright 2013 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.
 
 #ifndef ASH_METRICS_USER_METRICS_RECORDER_H_
 #define ASH_METRICS_USER_METRICS_RECORDER_H_
 
 #include "ash/ash_export.h"
 #include "ash/metrics/task_switch_metrics_recorder.h"
+#include "base/memory/scoped_ptr.h"
 #include "base/timer/timer.h"
 
 namespace ash {
 
+class UserMetricsRecorderProxy;
+
 namespace test {
 class UserMetricsRecorderTestAPI;
 }
 
 enum UserMetricsAction {
   UMA_ACCEL_EXIT_FIRST_Q,
   UMA_ACCEL_EXIT_SECOND_Q,
   UMA_ACCEL_KEYBOARD_BRIGHTNESS_DOWN_F6,
   UMA_ACCEL_KEYBOARD_BRIGHTNESS_UP_F7,
   UMA_ACCEL_LOCK_SCREEN_LOCK_BUTTON,
@@ skipping 133 matching lines @@
   friend class test::UserMetricsRecorderTestAPI;
 
   // Creates a UserMetricsRecorder and will only record periodic metrics if
   // |record_periodic_metrics| is true. This is used by tests that do not want
   // the timer to be started.
   // TODO(bruthig): Add a constructor that accepts a base::RepeatingTimer so
   // that tests can inject a test double that can be controlled by the test. The
   // missing piece is a suitable base::RepeatingTimer test double.
   explicit UserMetricsRecorder(bool record_periodic_metrics);
 
+  void Init(bool record_periodic_metrics);
+
   // Records UMA metrics. Invoked periodically by the |timer_|.
   void RecordPeriodicMetrics();
 
   // Returns true if the user's session is active and they are in a desktop
   // environment.
   bool IsUserInActiveDesktopEnvironment() const;
 
   // Starts the |timer_| and binds it to |RecordPeriodicMetrics|.
   void StartTimer();
 
   // The periodic timer that triggers metrics to be recorded.
   base::RepeatingTimer<UserMetricsRecorder> timer_;
 
   TaskSwitchMetricsRecorder task_switch_metrics_recorder_;
 
+  scoped_ptr<UserMetricsRecorderProxy> user_metrics_recorder_proxy_;
+
   DISALLOW_COPY_AND_ASSIGN(UserMetricsRecorder);
 };
 
 }  // namespace ash
 
 #endif  // ASH_METRICS_USER_METRICS_RECORDER_H_