Add tests for guest user events

Also, move ACTION_USER_GUEST_EXIT_CONFIRMED so it is only logged after
safety-check

Test: ROBOTEST_FILTER="com.android.settings.users.UserSettingsTest" m RunSettingsRoboTests
Test: ROBOTEST_FILTER="com.android.settings.users.UserDetailsSettingsTest" m RunSettingsRoboTests
Bug: 184200796
Change-Id: Id18aa914bbb262984d7c7cf4b8a4ffdde278fd23

src/com/android/settings/users/UserSettings.java

@@ -829,13 +829,14 @@ public class UserSettings extends SettingsPreferenceFragment
     /**
      * Erase the current user (guest) and switch to another user.
      */
-    private void exitGuest() {
+    @VisibleForTesting
+    void exitGuest() {
         // Just to be safe
-        mMetricsFeatureProvider.action(getActivity(),
-                SettingsEnums.ACTION_USER_GUEST_EXIT_CONFIRMED);
         if (!isCurrentUserGuest()) {
             return;
         }
+        mMetricsFeatureProvider.action(getActivity(),
+                SettingsEnums.ACTION_USER_GUEST_EXIT_CONFIRMED);
         removeThisUser();
     }