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

ash/metrics/task_switch_metrics_recorder.cc

 // Copyright 2015 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/task_switch_metrics_recorder.h"
 
 #include "ash/metrics/task_switch_time_tracker.h"
 
 namespace ash {
 
 namespace {
 
 const char kShelfHistogramName[] =
     "Ash.Shelf.TimeBetweenNavigateToTaskSwitches";
 
+const char kTabStripHistogramName[] =
+    "Ash.Tab.TimeBetweenSwitchToExistingTabUserActions";
+
 const char kAcceleratorWindowCycleHistogramName[] =
     "Ash.WindowCycleController.TimeBetweenTaskSwitches";
 
 // Returns the histogram name for the given |task_switch_source|.
 const char* GetHistogramName(
     TaskSwitchMetricsRecorder::TaskSwitchSource task_switch_source) {
   switch (task_switch_source) {
     case TaskSwitchMetricsRecorder::kShelf:
       return kShelfHistogramName;
+    case TaskSwitchMetricsRecorder::kTabStrip:
+      return kTabStripHistogramName;
     case TaskSwitchMetricsRecorder::kWindowCycleController:
       return kAcceleratorWindowCycleHistogramName;
   }
   NOTREACHED();
   return nullptr;
 }
 
 }  // namespace
 
 TaskSwitchMetricsRecorder::TaskSwitchMetricsRecorder() {
@@ skipping 26 matching lines @@
 
   const char* histogram_name = GetHistogramName(task_switch_source);
   DCHECK(histogram_name);
 
   histogram_map_.add(
       task_switch_source,
       make_scoped_ptr(new TaskSwitchTimeTracker(histogram_name)));
 }
 
 }  // namespace ash