Supporting Atomix classes for DocumentTree distributed primitive

Change-Id: I754222337401f90f976d4152b6abbdf2e1a4df8e
diff --git a/core/api/src/main/java/org/onosproject/store/service/DistributedPrimitive.java b/core/api/src/main/java/org/onosproject/store/service/DistributedPrimitive.java
index 8a2c7ba..5c93b54 100644
--- a/core/api/src/main/java/org/onosproject/store/service/DistributedPrimitive.java
+++ b/core/api/src/main/java/org/onosproject/store/service/DistributedPrimitive.java
@@ -72,6 +72,11 @@
         WORK_QUEUE,
 
         /**
+         * Document tree.
+         */
+        DOCUMENT_TREE,
+
+        /**
          * Distributed topic.
          */
         TOPIC,