Do not navigate to vm-connect page upon disconnect

runtime/bin/vmservice/observatory/lib/src/app/location_manager.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;
 
 abstract class LocationManager extends Observable {
   final _initialPath = '/vm';
   ObservatoryApplication _app;
 
@@ skipping 15 matching lines @@
     if (_lastUrl != url) {
       Logger.root.info('Navigated to ${url}');
       window.history.pushState(url, document.title, url);
       _lastUrl = url;
     }
   }
 
   /// Go to a specific url.
   void go(String url) {
     if (_app.vm == null) {
+      if (!window.confirm('Connection with VM has been lost. '
+                          'Proceeding will lose current page.')) {
+        return;
+      }
       url = makeLink('/vm-connect/');
     }
     _pushUrl(url);
     _go(url);
   }
 
   void _go(String url) {
     // Chop off leading '#'.
     if (url.startsWith('#')) {
       url = url.substring(1);
@@ skipping 78 matching lines @@
     _go(window.location.pathname);
   }
 
   void _onLocationChange(PopStateEvent _) {
     _go(window.location.pathname);
   }
 
   /// Given an application url, generate a link for an anchor tag.
   String makeLink(String url) => url;
 }