Ensure we run the observable transform on PolymerElement (fixes issue 14942)

pkg/observe/test/transformer_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:async';
 import 'package:barback/barback.dart';
-import 'package:observe/transform.dart';
+import 'package:observe/transformer.dart';
 import 'package:unittest/compact_vm_config.dart';
 import 'package:unittest/unittest.dart';
 
 main() {
   useCompactVMConfiguration();
 
   group('replaces Observable for ChangeNotifier', () {
     _testClause('extends Observable', 'extends ChangeNotifier');
     _testClause('extends Base with Observable',
         'extends Base with ChangeNotifier');
@@ skipping 189 matching lines @@
     "      Foo\n"
     "          get foo => __\$foo; Foo __\$foo/*D*/= 1; "
         "${_makeSetter('Foo', 'foo')} "
         "@reflectable @$meta @otherMetadata Foo get bar => __\$bar; "
         "Foo __\$bar =/*A*/2/*B*/; ${_makeSetter('Foo', 'bar')}\n"
     "          @reflectable @$meta @otherMetadata Foo get quux => __\$quux; "
         "Foo __\$quux/*C*/; ${_makeSetter('Foo', 'quux')}\n\n"
     "  @reflectable @$meta dynamic get baz => __\$baz; dynamic __\$baz; "
         "${_makeSetter('dynamic', 'baz')}\n"
     "}\n";