[Composition] Disallow composition for leaf types

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

platform/containment/test/CompositionModelPolicySpec.js

@@ -0,0 +1,26 @@
+/*global define,Promise,describe,it,expect,beforeEach,waitsFor,jasmine*/
+
+define(
+    ["../src/CompositionModelPolicy"],
+    function (CompositionModelPolicy) {
+        "use strict";
+
+        describe("The composition model policy", function () {
+            var mockType,
+                policy;
+
+            beforeEach(function () {
+                mockType = jasmine.createSpyObj('type', ['getInitialModel']);
+                policy = new CompositionModelPolicy();
+            });
+
+            it("only allows composition for types which will have a composition property", function () {
+                mockType.getInitialModel.andReturn({});
+                expect(policy.allow(mockType)).toBeFalsy();
+                mockType.getInitialModel.andReturn({ composition: [] });
+                expect(policy.allow(mockType)).toBeTruthy();
+            });
+        });
+
+    }
+);