Fix handling of VM reconnect

runtime/bin/vmservice/observatory/lib/src/app/application.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.
 
 part of app;
 
 /// The observatory application. Instances of this are created and owned
 /// by the observatory_application custom element.
 class ObservatoryApplication extends Observable {
   static ObservatoryApplication app;
@@ skipping 101 matching lines @@
 
   void _onError(ServiceError error) {
     lastErrorOrException = error;
     _visit('error/', null);
   }
 
   void _onException(ServiceException exception) {
     lastErrorOrException = exception;
     if (exception.kind == 'NetworkException') {
       // Got a network exception, visit the vm-connect page.
+      this.vm = null;
       locationManager.go(locationManager.makeLink('/vm-connect/'));
     } else {
       _visit('error/', null);
     }
   }
 
   void _visit(String url, String args) {
     var argsMap;
     if (args == null) {
       argsMap = {};
@@ skipping 85 matching lines @@
 
   _vmDisconnected(VM vm) {
     if (this.vm != vm) {
       // This disconnect event occured *after* a new VM was installed.
       return;
     }
     this.vm = null;
     notifications.add(new ServiceEvent.vmDisconencted());
   }
 }