Fix sort orders on longs.

The int conversion narrows a long possibly inverting its sign. This may
lead to broken comparator sort orders.
Caught by Error Prone.
Bug: 27723540

Change-Id: I53d70c25a22cdcfc496443395b170f586d259fa7

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

@@ -133,7 +133,7 @@ public class NotificationStation extends SettingsPreferenceFragment {
                 @Override
                 public int compare(HistoricalNotificationInfo lhs,
                                    HistoricalNotificationInfo rhs) {
-                    return (int)(rhs.timestamp - lhs.timestamp);
+                    return Long.compare(rhs.timestamp, lhs.timestamp);
                 }
             };