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

runtime/observatory/lib/src/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:polymer/polymer.dart';
 import 'package:observatory/service.dart';
 import 'service_ref.dart';
 
@@ skipping 36 matching lines @@
         ref = result;
         notifyPropertyChange(#ref, 0, 1);
       }).whenComplete(onDone);
     } else {
       Instance refMap = ref;
       refMap.fields = null;
       refMap.elements = null;
       onDone();
     }
   }
+
+  String makeExpandKey(String key) {
+    return '${expandKey}/${key}';
+  }
 }