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 e0fa0c3c626a1aa43ea154f55b6e02eb8ba8d260..a42f9b14f9fc59958c124c26d9a3658328a80b4d 100644
--- a/runtime/observatory/lib/elements.dart
+++ b/runtime/observatory/lib/elements.dart
@@ -55,6 +55,8 @@ 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';
@@ -90,6 +92,8 @@ 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';
+export 'package:observatory/src/elements/containers/virtual_tree.dart';
 export 'package:observatory/src/elements/curly_block.dart';
 export 'package:observatory/src/elements/isolate_ref.dart';
 export 'package:observatory/src/elements/nav/bar.dart';
@@ -143,6 +147,8 @@ Future initElements() async {
   SourceLinkElement.tag.ensureRegistration();
   SourceLinkElementWrapper.tag.ensureRegistration();
   ViewFooterElement.tag.ensureRegistration();
+  VirtualCollectionElement.tag.ensureRegistration();
+  VirtualTreeElement.tag.ensureRegistration();
   VMConnectElement.tag.ensureRegistration();
   VMConnectTargetElement.tag.ensureRegistration();
 }