ONOS-3539 Insert optional delay for showing highlights

Change-Id: I289d54fc2b401da397fa97e912e98177d108df23
diff --git a/core/api/src/main/java/org/onosproject/ui/topo/TopoJson.java b/core/api/src/main/java/org/onosproject/ui/topo/TopoJson.java
index efe69f5..bd07d6c 100644
--- a/core/api/src/main/java/org/onosproject/ui/topo/TopoJson.java
+++ b/core/api/src/main/java/org/onosproject/ui/topo/TopoJson.java
@@ -33,6 +33,7 @@
     static final String HOSTS = "hosts";
     static final String LINKS = "links";
     static final String SUBDUE = "subdue";
+    static final String DELAY = "delay";
 
     static final String ID = "id";
     static final String LABEL = "label";
@@ -99,6 +100,10 @@
         if (!toSubdue.equals(Highlights.Amount.ZERO)) {
             payload.put(SUBDUE, toSubdue.toString());
         }
+        int delay = highlights.delayMs();
+        if (delay > 0) {
+            payload.put(DELAY, delay);
+        }
         return payload;
     }