Add enum completion

Change-Id: I5ee7d6359812535d0eef9f70e1b66e205d93cf39
diff --git a/src/schema.hpp b/src/schema.hpp
index e1f019f..c55e659 100644
--- a/src/schema.hpp
+++ b/src/schema.hpp
@@ -79,6 +79,7 @@
     virtual bool nodeExists(const std::string& location, const std::string& node) const = 0;
     virtual const std::set<std::string> listKeys(const schemaPath_& location, const ModuleNodePair& node) const = 0;
     virtual yang::LeafDataTypes leafType(const schemaPath_& location, const ModuleNodePair& node) const = 0;
+    virtual const std::set<std::string> enumValues(const schemaPath_& location, const ModuleNodePair& node) const = 0;
     virtual std::set<std::string> childNodes(const schemaPath_& path, const Recursion recursion) const = 0;
 
 private: