[polymer] fix editor hints -- query/queryAll and unused imports

pkg/polymer/test/instance_attrs_test.dart

Index: pkg/polymer/test/instance_attrs_test.dart
diff --git a/pkg/polymer/test/instance_attrs_test.dart b/pkg/polymer/test/instance_attrs_test.dart
index a759ae9d028fbeb5deff7385afc154ef8f675c7d..f5b6eac7b9d4c3cb677a5da3990e8a05784b6b59 100644
--- a/pkg/polymer/test/instance_attrs_test.dart
+++ b/pkg/polymer/test/instance_attrs_test.dart
@@ -24,7 +24,7 @@ main() {
   setUp(() => Polymer.onReady);
 
   test('attributes were deserialized', () {
-    var elem = query('my-element');
+    var elem = querySelector('my-element');
 
     expect(elem.attributes, {'foo': '123', 'bar': 'hi', 'baz': 'world'},
         reason: 'attributes should be copied to instance');