Added UMA metrics for the system update UI in the status area.

ash/metrics/user_metrics_recorder.cc

Index: ash/metrics/user_metrics_recorder.cc
diff --git a/ash/metrics/user_metrics_recorder.cc b/ash/metrics/user_metrics_recorder.cc
index a820dbf55bc9311ba2412bde4fb16aed1a20f81f..b39ab07256f79f37be562ed023f089f8b26ee190 100644
--- a/ash/metrics/user_metrics_recorder.cc
+++ b/ash/metrics/user_metrics_recorder.cc
@@ -495,6 +495,10 @@ void UserMetricsRecorder::RecordUserMetricsAction(UserMetricsAction action) {
       base::RecordAction(
           base::UserMetricsAction("StatusArea_Network_Settings"));
       break;
+    case UMA_STATUS_AREA_OS_UPDATE_DEFAULT_SELECTED:
+      base::RecordAction(
+          base::UserMetricsAction("StatusArea_OS_Update_Default_Selected"));
+      break;
     case UMA_STATUS_AREA_SHOW_NETWORK_CONNECTION_DETAILS:
       base::RecordAction(
           base::UserMetricsAction("StatusArea_Network_ConnectionDetails"));