Record time between selecting items from the Ash app list

ash/metrics/task_switch_metrics_recorder.h

Index: ash/metrics/task_switch_metrics_recorder.h
diff --git a/ash/metrics/task_switch_metrics_recorder.h b/ash/metrics/task_switch_metrics_recorder.h
index 8d5a881b69893b7512e54b5ad9dda3ee7b058c50..b2103be01d7a27a036cec32b1feaf9123f57db25 100644
--- a/ash/metrics/task_switch_metrics_recorder.h
+++ b/ash/metrics/task_switch_metrics_recorder.h
@@ -22,6 +22,8 @@ class ASH_EXPORT TaskSwitchMetricsRecorder {
   // Enumeration of the different user interfaces that could be the source of
   // a task switch. Note this is not necessarily comprehensive of all sources.
   enum TaskSwitchSource {
+    // Task switches from selecting items in the app list.
+    kAppList,
     // Task switches caused by selecting a window from overview mode which is
     // different from the previously-active window.
     kOverviewMode,