Added metrics to track the time between task switches done via the shelf.

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/timer/timer.h"
 
 namespace ash {
 
 namespace test {
 class UserMetricsRecorderTestAPI;
 }
 
 enum UserMetricsAction {
   UMA_ACCEL_EXIT_FIRST_Q,
@@ skipping 142 matching lines @@
   // 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_;
+
   DISALLOW_COPY_AND_ASSIGN(UserMetricsRecorder);
 };
 
 }  // namespace ash
 
 #endif  // ASH_METRICS_USER_METRICS_RECORDER_H_