Log visibility change for DialogCreatable in Settings.

Bug: 30681529
Test: adb logcat -b events | egrep "(sysui_|notification_)"
Test: make RunSettingsRoboTests
Change-Id: I51754d258ba1ddfae24323681f21cd02de4dbb4e

src/com/android/settings/display/NightDisplaySettings.java

@@ -155,6 +155,17 @@ public class NightDisplaySettings extends SettingsPreferenceFragment
         return super.onCreateDialog(dialogId);
     }
 
+    @Override
+    public int getDialogMetricsCategory(int dialogId) {
+        switch (dialogId) {
+            case DIALOG_START_TIME:
+                return MetricsEvent.DIALOG_NIGHT_DISPLAY_SET_START_TIME;
+            case DIALOG_END_TIME:
+                return MetricsEvent.DIALOG_NIGHT_DISPLAY_SET_END_TIME;
+            default:
+                return 0;
+        }
+    }
     @Override
     public void onActivated(boolean activated) {
         mActivatedPreference.setChecked(activated);