Introduce IMPORTANCE_MIN.

Bug: 22960980
Change-Id: Ia3876e0b3b5dae19553fd467313b46408fcbb0f4

src/com/android/settings/notification/NotificationStation.java

@@ -109,6 +109,11 @@ public class NotificationStation extends SettingsPreferenceFragment {
         public void onNotificationRankingUpdate(RankingMap ranking) {
             mRanking = ranking;
         }
+
+        @Override
+        public void onListenerConnected() {
+            mRanking = getCurrentRanking();
+        }
     };
 
     private Context mContext;