Persist data to disk when system shuts down

Test: local test

BUG: b/112432890

Change-Id: Iaed318671a719cc366d4e6be9f77270147ba6596
diff --git a/cmds/statsd/src/StatsService.h b/cmds/statsd/src/StatsService.h
index 1f1d782..cbf3429 100644
--- a/cmds/statsd/src/StatsService.h
+++ b/cmds/statsd/src/StatsService.h
@@ -84,6 +84,11 @@
     void Startup();
 
     /**
+     * Called when terminiation signal received.
+     */
+    void Terminate();
+
+    /**
      * Called by LogReader when there's a log event to process.
      */
     virtual void OnLogEvent(LogEvent* event);