Fixed custom elements to work in Polymer

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index b581f65c8b827f0d2579d46979f51d5789803cd9..7bef67f625f66818dffa3ad863fbce92682c3a54 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -122,6 +122,11 @@ Future<Isolate> spawnDomUri(Uri uri, List<String> args, message) {
   // TODO(17738): Implement this.
   throw new UnimplementedError();
 }
+
+/// Dartium functions that are a NOOP in dart2js.
+unwrap_jso(dartClass_instance) => dartClass_instance;
+wrap_jso(jsObject) => jsObject;
+createCustomUpgrader(Type customElementClass, $this) => $this;
 // 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.