Build Observatory with runtime

runtime/observatory/lib/src/elements/action_link.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.
 
 library action_link_element;
 
 import 'package:polymer/polymer.dart';
 
 @CustomTag('action-link')
 class ActionLinkElement extends PolymerElement {
@@ skipping 11 matching lines @@
     if (callback != null) {
       busy = true;
       // TODO(turnidge): Track down why adding a dummy argument makes
       // this work but having a no-argument callback doesn't.
       callback(null).whenComplete(() {
           busy = false;
         });
     }
   }
 }