Improve VM connection flow in Observatory

runtime/observatory/lib/src/repositories/target.dart

 // Copyright (c) 2016, 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 repositories;
 
 class TargetChangeEvent implements M.TargetChangeEvent {
   final TargetRepository repository;
-  TargetChangeEvent(this.repository);
+  final bool disconnected;
+  TargetChangeEvent(this.repository, [this.disconnected = false]);
 }
 
 class TargetRepository implements M.TargetRepository {
 
   static const _historyKey = 'history';
 
   final StreamController<TargetChangeEvent> _onChange;
   final Stream<TargetChangeEvent> onChange;
   final SettingsRepository _settings = new SettingsRepository('targetManager');
 
   final List<SC.WebSocketVMTarget> _list = <SC.WebSocketVMTarget>[];
   SC.WebSocketVMTarget current;
 
   factory TargetRepository() {
     var controller = new StreamController<TargetChangeEvent>();
     var stream = controller.stream.asBroadcastStream();
     return new TargetRepository._(controller, stream);
   }
 
   TargetRepository._(this._onChange, this.onChange) {
     _restore();
-    if (_list.isEmpty) {
-      _list.add(new SC.WebSocketVMTarget(_networkAddressOfDefaultTarget()));
+    // Add the default address if it doesn't already exist.
+    if (_find(_networkAddressOfDefaultTarget()) == null) {
+      add(_networkAddressOfDefaultTarget());
     }
-    current = _list.first;
+    // Set the current target to the default target.
+    current = _find(_networkAddressOfDefaultTarget());
   }
 
   void add(String address) {
-    if (_find(address) != null) return;
+    if (_find(address) != null) {
+      return;
+    }
     _list.insert(0, new SC.WebSocketVMTarget(address));
     _onChange.add(new TargetChangeEvent(this));
     _store();
   }
 
   Iterable<SC.WebSocketVMTarget> list() => _list;
 
   void setCurrent(M.Target t) {
     SC.WebSocketVMTarget target = t as SC.WebSocketVMTarget;
-    if (!_list.contains(target)) return;
+    if (!_list.contains(target)) {
+      return;
+    }
     current = target;
     current.lastConnectionTime = new DateTime.now().millisecondsSinceEpoch;
     _onChange.add(new TargetChangeEvent(this));
     _store();
   }
 
+  void emitDisconnectEvent() {
+    _onChange.add(new TargetChangeEvent(this, true));
+  }
+
   void delete(o) {
     if (_list.remove(o)) {
       if (o == current) {
         current = null;
       }
       _onChange.add(new TargetChangeEvent(this));
       _store();
     }
   }
 
@@ skipping 30 matching lines @@
       // We are running as JavaScript, use the same host that Observatory has
       // been loaded from.
       return 'ws://${window.location.host}/ws';
     } else {
       // Otherwise, assume we are running from Dart Editor and want to connect
       // to the default host.
       return 'ws://localhost:8181/ws';
     }
   }
 }