Starting to experiment with flow tracking.
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/topology/impl/DistributedTopologyStore.java b/core/store/dist/src/main/java/org/onlab/onos/store/topology/impl/DistributedTopologyStore.java
index 567861e..9ae9d7b 100644
--- a/core/store/dist/src/main/java/org/onlab/onos/store/topology/impl/DistributedTopologyStore.java
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/topology/impl/DistributedTopologyStore.java
@@ -125,7 +125,8 @@
         // Promote the new topology to current and return a ready-to-send event.
         synchronized (this) {
             current = newTopology;
-            return new TopologyEvent(TopologyEvent.Type.TOPOLOGY_CHANGED, current);
+            return new TopologyEvent(TopologyEvent.Type.TOPOLOGY_CHANGED,
+                                     current, reasons);
         }
     }