[Composition] Disallow composition for leaf types

Disallow composition for domain object types which will
not have a composition property; WTD-1221.

platform/containment/src/CompositionModelPolicy.js

@@ -0,0 +1,28 @@
+/*global define*/
+
+define(
+    [],
+    function () {
+        "use strict";
+
+        /**
+         * Policy allowing composition only for domain object types which
+         * have a composition property.
+         */
+        function CompositionModelPolicy() {
+            return {
+                /**
+                 * Is the type identified by the candidate allowed to
+                 * contain the type described by the context?
+                 */
+                allow: function (candidate, context) {
+                    return Array.isArray(
+                        (candidate.getInitialModel() || {}).composition
+                    );
+                }
+            };
+        }
+
+        return CompositionModelPolicy;
+    }
+);