Added new implementations for virtual containers

runtime/observatory/lib/elements.dart

 library observatory_elements;
 
 // Export elements.
 export 'package:observatory/src/elements/action_link.dart';
 export 'package:observatory/src/elements/class_ref.dart';
 export 'package:observatory/src/elements/class_tree.dart';
 export 'package:observatory/src/elements/class_view.dart';
 export 'package:observatory/src/elements/code_ref.dart';
 export 'package:observatory/src/elements/code_view.dart';
 export 'package:observatory/src/elements/context_ref.dart';
@@ skipping 37 matching lines @@
 export 'package:observatory/src/elements/script_inset.dart';
 export 'package:observatory/src/elements/script_view.dart';
 export 'package:observatory/src/elements/service_ref.dart';
 export 'package:observatory/src/elements/service_view.dart';
 export 'package:observatory/src/elements/timeline_page.dart';
 export 'package:observatory/src/elements/vm_connect.dart';
 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';
 import 'package:observatory/src/elements/isolate_ref_wrapper.dart';
 import 'package:observatory/src/elements/nav/bar.dart';
 import 'package:observatory/src/elements/nav/class_menu.dart';
 import 'package:observatory/src/elements/nav/class_menu_wrapper.dart';
 import 'package:observatory/src/elements/nav/isolate_menu.dart';
 import 'package:observatory/src/elements/nav/isolate_menu_wrapper.dart';
 import 'package:observatory/src/elements/nav/library_menu.dart';
@@ skipping 15 matching lines @@
 import 'package:observatory/src/elements/script_ref.dart';
 import 'package:observatory/src/elements/script_ref_wrapper.dart';
 import 'package:observatory/src/elements/source_link.dart';
 import 'package:observatory/src/elements/source_link_wrapper.dart';
 import 'package:observatory/src/elements/view_footer.dart';
 import 'package:observatory/src/elements/vm_connect_target.dart';
 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';
 export 'package:observatory/src/elements/nav/class_menu.dart';
 export 'package:observatory/src/elements/nav/isolate_menu.dart';
 export 'package:observatory/src/elements/nav/library_menu.dart';
 export 'package:observatory/src/elements/nav/menu.dart';
 export 'package:observatory/src/elements/nav/menu_item.dart';
 export 'package:observatory/src/elements/nav/notify.dart';
 export 'package:observatory/src/elements/nav/notify_event.dart';
@@ skipping 33 matching lines @@
   NavRefreshElementWrapper.tag.ensureRegistration();
   NavTopMenuElement.tag.ensureRegistration();
   NavTopMenuElementWrapper.tag.ensureRegistration();
   NavVMMenuElement.tag.ensureRegistration();
   NavVMMenuElementWrapper.tag.ensureRegistration();
   ScriptRefElement.tag.ensureRegistration();
   ScriptRefElementWrapper.tag.ensureRegistration();
   SourceLinkElement.tag.ensureRegistration();
   SourceLinkElementWrapper.tag.ensureRegistration();
   ViewFooterElement.tag.ensureRegistration();
+  VirtualCollectionElement.tag.ensureRegistration();
+  VirtualTreeElement.tag.ensureRegistration();
   VMConnectElement.tag.ensureRegistration();
   VMConnectTargetElement.tag.ensureRegistration();
 }