Add support for asynchronous event notification to the observatory.

runtime/bin/vmservice/client/lib/src/elements/nav_bar.dart

Index: runtime/bin/vmservice/client/lib/src/elements/nav_bar.dart
diff --git a/runtime/bin/vmservice/client/lib/src/elements/nav_bar.dart b/runtime/bin/vmservice/client/lib/src/elements/nav_bar.dart
index 87e7e3563f93c165fc43f26ae056a250e8068631..b315b4bb4ea6b0db1f3730b9fa58ef496dcd1522 100644
--- a/runtime/bin/vmservice/client/lib/src/elements/nav_bar.dart
+++ b/runtime/bin/vmservice/client/lib/src/elements/nav_bar.dart
@@ -116,3 +116,22 @@ class ClassNavMenuElement extends ObservatoryElement {
 
   ClassNavMenuElement.created() : super.created();
 }
+
+@CustomTag('nav-notify')
+class NavNotifyElement extends ObservatoryElement {
+  @published ObservableList<ServiceEvent> events;
+  
+  NavNotifyElement.created() : super.created();
+}
+
+@CustomTag('nav-notify-item')
+class NavNotifyItemElement extends ObservatoryElement {
+  @published ObservableList<ServiceEvent> events;
+  @published ServiceEvent event;
+  
+  void closeItem(MouseEvent e, var detail, Element target) {
+    events.remove(event);
+  }
+
+  NavNotifyItemElement.created() : super.created();
+}