Yesterday's deadlock fix was wrong. It could drop notifications.

runtime/observatory/lib/src/elements/debugger.dart

 // Copyright (c) 2014, 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 debugger_page_element;
 
 import 'dart:async';
 import 'dart:html';
 import 'observatory_element.dart';
 import 'package:observatory/cli.dart';
@@ skipping 102 matching lines @@
     if (args.length < 1) {
       debugger.console.print('print expects arguments');
       return new Future.value(null);
     }
     var expr = args.join('');
     return debugger.isolate.evalFrame(debugger.currentFrame, expr)
       .then((response) {
           if (response is DartError) {
             debugger.console.print(response.message);
           } else {
-            ServiceMap instance = response;
             debugger.console.print('= ', newline:false);
-            debugger.console.printRef(instance);
+            debugger.console.printRef(response);
           }
       });
   }
 
   String helpShort = 'Evaluate and print an expression in the current frame';
 
   String helpLong =
       'Evaluate and print an expression in the current frame.\n'
       '\n'
       'Syntax: print <expression>\n'
@@ skipping 1133 matching lines @@
     var span = new SpanElement();
     span.classes.add('bold');
     span.appendText(line);
     if (newline) {
       span.appendText('\n');
     }
     $['consoleText'].children.add(span);
     span.scrollIntoView();
   }
 
-  void printRef(ServiceMap ref, { bool newline:true }) {
+  void printRef(Instance ref, { bool newline:true }) {
     var refElement = new Element.tag('instance-ref');
     refElement.ref = ref;
     $['consoleText'].children.add(refElement);
     if (newline) {
       this.newline();
     }
     refElement.scrollIntoView();
   }
 
   void newline() {
@@ skipping 57 matching lines @@
           default:
             busy = false;
             break;
         }
       });
   }
 
   DebuggerInputElement.created() : super.created();
 }