Added new implementations for virtual containers

runtime/observatory/lib/src/elements/helpers/rendering_scheduler.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.
 
 import 'dart:async';
 
 import 'package:observatory/src/elements/helpers/rendering_queue.dart';
 export 'package:observatory/src/elements/helpers/rendering_queue.dart';
 
 /// A generic renderable object.
@@ skipping 17 matching lines @@
 /// Scheduler for rendering operations.
 class RenderingScheduler<T extends Renderable> implements RenderingTask {
   bool _enabled = false;
   bool _dirty = false;
   bool _renderingScheduled = false;
   bool _notificationScheduled = false;
   /// Element managed by this scheduler.
   final T element;
   /// Queue used for rendering operations.
   final RenderingQueue queue;
+  /// Does the element need a new rendering cycle.
+  bool get isDirty => _dirty;
+  /// Is the scheduler enabled.
+  bool get isEnabled => _enabled;
 
   final StreamController<RenderedEvent<T>> _onRendered =
-                            new StreamController<RenderedEvent<T>>.broadcast();
+      new StreamController<RenderedEvent<T>>.broadcast();
   Stream<RenderedEvent<T>> get onRendered => _onRendered.stream;
 
   /// Creates a new scheduler for an element.
   /// If no queue is provided it will create a new default configured queue.
   factory RenderingScheduler(T element, {RenderingQueue queue}) {
     assert(element != null);
     if (queue == null) { queue = new RenderingQueue(); }
     return new RenderingScheduler<T>._(element, queue);
   }
 
@@ skipping 57 matching lines @@
     if (_notificationScheduled) return;
     _notify();
     _notificationScheduled = true;
   }
 
   Future _notify() async {
     _onRendered.add(new RenderedEvent<T>(element, _dirty));
     _notificationScheduled = false;
   }
 }