fix test case in 5d17efc

test/unit/styling-cross-scope-var.html

@@ -491,8 +491,10 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
     </style>
   </template>
   <script>
-    Polymer({
-      is: 'x-variable-override'
+    HTMLImports.whenReady(function() {
+      Polymer({
+        is: 'x-variable-override'
+      });
     });
   </script>
 </dom-module>