Using provider pattern for cluster metadata.

Change-Id: I5a572b3df9149be959dde9868a9c594dec26a3e0
diff --git a/core/api/src/main/java/org/onosproject/cluster/ClusterMetadataProviderService.java b/core/api/src/main/java/org/onosproject/cluster/ClusterMetadataProviderService.java
new file mode 100644
index 0000000..d8e15e6
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+++ b/core/api/src/main/java/org/onosproject/cluster/ClusterMetadataProviderService.java
@@ -0,0 +1,39 @@
+/*
+ * Copyright 2015-2016 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.cluster;
+
+import org.onosproject.net.provider.ProviderService;
+import org.onosproject.store.service.Versioned;
+
+/**
+ * Service through which a {@link ClusterMetadataProvider provider} can notify core of
+ * updates made to cluster metadata.
+ */
+public interface ClusterMetadataProviderService extends ProviderService<ClusterMetadataProvider> {
+
+    /**
+     * Notifies about a change to cluster metadata.
+     * @param newMetadata new cluster metadata value
+     */
+    void clusterMetadataChanged(Versioned<ClusterMetadata> newMetadata);
+
+    /**
+     * Notifies that a node just become the active member of a partition.
+     * @param partitionId partition identifier
+     * @param nodeId identifier of node
+     */
+    void newActiveMemberForPartition(PartitionId partitionId, NodeId nodeId);
+}