public boolean dependsOn(ModelNode node, ModelNode sortedNode) {
            return map.get(node.id).contains(sortedNode.id);
        }
Performs a topological sort ot the models stored in this graph. The algorithm is based on Kahn topological sort.

@return a sorted list of {@link com.yahoo.config.model.graph.ModelNode} in dependency order.
config-model/src/main/java/com/yahoo/config/model/graph/ModelGraph.java