polymer warning clean

pkg/polymer/test/publish_attributes_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:html';
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_config.dart';
 import 'package:polymer/polymer.dart';
 
 // Dart note: unlike JS, you can't publish something that doesn't
@@ skipping 30 matching lines @@
   @published int squid = 7;
 }
 
 main() {
   initPolymer();
   useHtmlConfiguration();
 
   setUp(() => Polymer.onReady);
 
   test('published properties', () {
-    published(tag) =>
-        query('polymer-element[name=$tag]').publishedProperties;
+    published(tag) => (query('polymer-element[name=$tag]')
+        as PolymerDeclaration).publishedProperties;
 
     expect(published('x-foo'), [#Foo, #baz]);
     expect(published('x-bar'), [#Foo, #baz, #Bar]);
     expect(published('x-zot'), [#Foo, #baz, #Bar, #zot]);
     expect(published('x-squid'), [#Foo, #baz, #Bar, #zot, #squid]);
   });
 }