[CORD-2937] Improve work partition on Multicast

Change-Id: Ia8761245e7f199721c1228bfd500e0392a20de05
(cherry picked from commit 901851ef9f2a53d6fdd08d0cc1232b125f1e35bf)
diff --git a/apps/segmentrouting/app/src/main/java/org/onosproject/segmentrouting/SegmentRoutingService.java b/apps/segmentrouting/app/src/main/java/org/onosproject/segmentrouting/SegmentRoutingService.java
index b688726..aabed47 100644
--- a/apps/segmentrouting/app/src/main/java/org/onosproject/segmentrouting/SegmentRoutingService.java
+++ b/apps/segmentrouting/app/src/main/java/org/onosproject/segmentrouting/SegmentRoutingService.java
@@ -17,6 +17,7 @@
 
 import org.onlab.packet.IpAddress;
 import org.onlab.packet.IpPrefix;
+import org.onosproject.cluster.NodeId;
 import org.onosproject.net.ConnectPoint;
 import org.onosproject.net.DeviceId;
 import org.onosproject.net.Link;
@@ -247,4 +248,11 @@
      */
     Map<ConnectPoint, List<ConnectPoint>> getMcastPaths(IpAddress mcastIp);
 
+    /**
+     * Return the leaders of the mcast groups.
+     *
+     * @param mcastIp the group ip
+     * @return the mapping group-node
+     */
+    Map<IpAddress, NodeId> getMcastLeaders(IpAddress mcastIp);
 }