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

ash/metrics/user_metrics_recorder.cc

 // 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.
 
 #include "ash/metrics/user_metrics_recorder.h"
 
 #include "ash/session/session_state_delegate.h"
 #include "ash/shelf/shelf_layout_manager.h"
 #include "ash/shelf/shelf_view.h"
 #include "ash/shelf/shelf_widget.h"
@@ skipping 213 matching lines @@
       break;
     case ash::UMA_LAUNCHER_CLICK_ON_APP:
       base::RecordAction(base::UserMetricsAction("Launcher_ClickOnApp"));
       break;
     case ash::UMA_LAUNCHER_CLICK_ON_APPLIST_BUTTON:
       base::RecordAction(
           base::UserMetricsAction("Launcher_ClickOnApplistButton"));
       break;
     case ash::UMA_LAUNCHER_LAUNCH_TASK:
       base::RecordAction(base::UserMetricsAction("Launcher_LaunchTask"));
+      task_switch_metrics_recorder_.OnTaskSwitch(
+          TaskSwitchMetricsRecorder::kShelf);
       break;
     case ash::UMA_LAUNCHER_MINIMIZE_TASK:
       base::RecordAction(base::UserMetricsAction("Launcher_MinimizeTask"));
       break;
     case ash::UMA_LAUNCHER_SWITCH_TASK:
       base::RecordAction(base::UserMetricsAction("Launcher_SwitchTask"));
+      task_switch_metrics_recorder_.OnTaskSwitch(
+          TaskSwitchMetricsRecorder::kShelf);
       break;
     case UMA_MAXIMIZE_MODE_DISABLED:
       base::RecordAction(base::UserMetricsAction("Touchview_Disabled"));
       break;
     case UMA_MAXIMIZE_MODE_ENABLED:
       base::RecordAction(base::UserMetricsAction("Touchview_Enabled"));
       break;
     case UMA_MAXIMIZE_MODE_INITIALLY_DISABLED:
       base::RecordAction(
           base::UserMetricsAction("Touchview_Initially_Disabled"));
@@ skipping 341 matching lines @@
   return IsUserActive() && !IsKioskModeActive();
 }
 
 void UserMetricsRecorder::StartTimer() {
   timer_.Start(FROM_HERE,
                base::TimeDelta::FromSeconds(kAshPeriodicMetricsTimeInSeconds),
                this, &UserMetricsRecorder::RecordPeriodicMetrics);
 }
 
 }  // namespace ash