Added new implementations for virtual containers

runtime/observatory/lib/elements.dart

Index: runtime/observatory/lib/elements.dart
diff --git a/runtime/observatory/lib/elements.dart b/runtime/observatory/lib/elements.dart
index 4d9786e74fba1e43ff1cc0c2599f572569ec5d0c..24de9635dd00d1c484865c6e82545efd902de4d1 100644
--- a/runtime/observatory/lib/elements.dart
+++ b/runtime/observatory/lib/elements.dart
@@ -56,6 +56,8 @@ export 'package:observatory/src/elements/vm_view.dart';
 
 import 'dart:async';
 
+import 'package:observatory/src/elements/containers/virtual_collection.dart';
+import 'package:observatory/src/elements/containers/virtual_tree.dart';
 import 'package:observatory/src/elements/curly_block.dart';
 import 'package:observatory/src/elements/curly_block_wrapper.dart';
 import 'package:observatory/src/elements/isolate_ref.dart';
@@ -87,6 +89,10 @@ import 'package:observatory/src/elements/vm_connect.dart';
 
 export 'package:observatory/src/elements/helpers/rendering_queue.dart';
 
+export 'package:observatory/src/elements/containers/virtual_collection.dart'
+    hide CreateElementCallback, UpdateElementCallback;
+export 'package:observatory/src/elements/containers/virtual_tree.dart'
+    hide CreateElementCallback, UpdateElementCallback, GetChildrenCallback;
 export 'package:observatory/src/elements/curly_block.dart';
 export 'package:observatory/src/elements/isolate_ref.dart';
 export 'package:observatory/src/elements/nav/bar.dart';
@@ -134,6 +140,8 @@ Future initElements() async {
   NavVMMenuElement.tag.ensureRegistration();
   NavVMMenuElementWrapper.tag.ensureRegistration();
   ViewFooterElement.tag.ensureRegistration();
+  VirtualCollectionElement.tag.ensureRegistration();
+  VirtualTreeElement.tag.ensureRegistration();
   VMConnectElement.tag.ensureRegistration();
   VMConnectTargetElement.tag.ensureRegistration();
 }