Remember when a variable has been expanded/unexpanded in the debugger.

runtime/observatory/lib/src/elements/service_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 service_ref_element;
 
 import 'dart:html';
 import 'package:logging/logging.dart';
 import 'package:polymer/polymer.dart';
 import 'observatory_element.dart';
 import 'package:observatory/service.dart';
 
 @CustomTag('service-ref')
 class ServiceRefElement extends ObservatoryElement {
   @published ServiceObject ref;
   @published bool internal = false;
+  @published String expandKey;
   ServiceRefElement.created() : super.created();
 
   void refChanged(oldValue) {
     notifyPropertyChange(#url, "", url);
     notifyPropertyChange(#name, [], name);
     notifyPropertyChange(#nameIsEmpty, 0, 1);
     notifyPropertyChange(#hoverText, "", hoverText);
   }
 
   String get url {
@@ skipping 27 matching lines @@
   // Workaround isEmpty not being useable due to missing @MirrorsUsed.
   bool get nameIsEmpty {
     return (name == null) || name.isEmpty;
   }
 }
 
 
 @CustomTag('any-service-ref')
 class AnyServiceRefElement extends ObservatoryElement {
   @published ServiceObject ref;
+  @published String expandKey;
   AnyServiceRefElement.created() : super.created();
 
   Element _constructElementForRef() {
     var type = ref.type;
     switch (type) {
      case 'Class':
         ServiceRefElement element = new Element.tag('class-ref');
         element.ref = ref;
         return element;
       case 'Code':
@@ skipping 25 matching lines @@
         element.ref = ref;
         return element;
       case 'Script':
         ServiceRefElement element = new Element.tag('script-ref');
         element.ref = ref;
         return element;
       case 'Instance':
       case 'Sentinel':
         ServiceRefElement element = new Element.tag('instance-ref');
         element.ref = ref;
+        if (expandKey != null) {
+          element.expandKey = expandKey;
+        }
         return element;
       default:
         SpanElement element = new Element.tag('span');
         element.text = "<<Unknown service ref: $ref>>";
         return element;
     }
   }
 
   refChanged(oldValue) {
     // Remove the current view.
     children.clear();
     if (ref == null) {
       Logger.root.info('Viewing null object.');
       return;
     }
     var type = ref.type;
     var element = _constructElementForRef();
     if (element == null) {
       Logger.root.info('Unable to find a ref element for \'${type}\'');
       return;
     }
     children.add(element);
   }
 }
 
 @CustomTag('object-ref')
 class ObjectRefElement extends ServiceRefElement {
   ObjectRefElement.created() : super.created();
 }