Record time between selecting items from the Ash app list

ash/metrics/task_switch_metrics_recorder.cc

Index: ash/metrics/task_switch_metrics_recorder.cc
diff --git a/ash/metrics/task_switch_metrics_recorder.cc b/ash/metrics/task_switch_metrics_recorder.cc
index 3ac604798ba7ee57b8fc31a6e10066bff65abe16..b8b57fe4753606428c68f2be1236c100070d10c9 100644
--- a/ash/metrics/task_switch_metrics_recorder.cc
+++ b/ash/metrics/task_switch_metrics_recorder.cc
@@ -19,6 +19,8 @@ const char kTabStripHistogramName[] =
 const char kAcceleratorWindowCycleHistogramName[] =
     "Ash.WindowCycleController.TimeBetweenTaskSwitches";
 
+const char kAppListHistogramName[] = "Ash.AppList.TimeBetweenTaskSwitches";
+
 const char kOverviewModeHistogramName[] =
     "Ash.WindowSelector.TimeBetweenActiveWindowChanges";
 
@@ -26,6 +28,8 @@ const char kOverviewModeHistogramName[] =
 const char* GetHistogramName(
     TaskSwitchMetricsRecorder::TaskSwitchSource task_switch_source) {
   switch (task_switch_source) {
+    case TaskSwitchMetricsRecorder::kAppList:
+      return kAppListHistogramName;
     case TaskSwitchMetricsRecorder::kOverviewMode:
       return kOverviewModeHistogramName;
     case TaskSwitchMetricsRecorder::kShelf: