Add refresh button to stack trace page.

runtime/bin/vmservice/client/lib/src/observatory_elements/instance_ref.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 instance_ref_element;
 
 import 'package:logging/logging.dart';
 import 'package:polymer/polymer.dart';
 import 'service_ref.dart';
 
@@ skipping 10 matching lines @@
     return ref['preview'];
   }
 
   void toggleExpand(var a, var b, var c) {
     if (expanded) {
       ref['fields'] = null;
       ref['elements'] = null;
       expanded = false;
     } else {
       app.requestManager.requestMap(url).then((map) {
-          print(map);
           ref['fields'] = map['fields'];
           ref['elements'] = map['elements'];
           ref['length'] = map['length'];
           expanded = true;
       }).catchError((e, trace) {
           Logger.root.severe('Error while expanding instance-ref: $e\n$trace');
       });
     }
   }
 }