[Effen] Reduce splashes when scrolling.

sky/framework/fn.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 library fn;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:sky' as sky;
 import 'reflect.dart' as reflect;
@@ skipping 44 matching lines @@
 
 enum _SyncOperation { IDENTICAL, INSERTION, STATEFUL, STATELESS, REMOVAL }
 
 /*
  * All Effen nodes derive from UINode. All nodes have a _parent, a _key and
  * can be sync'd.
  */
 abstract class UINode {
   String _key;
   UINode _parent;
+  UINode get parent => _parent;
   sky.Node _root;
   bool _defunct = false;
 
   UINode({ Object key }) {
     _key = key == null ? "$runtimeType" : "$runtimeType-$key";
   }
 
   // Subclasses which implements Nodes that become stateful may return true
   // if the |old| node has become stateful and should be retained.
   bool _willSync(UINode old) => false;
 
   void _sync(UINode old, sky.ParentNode host, sky.Node insertBefore);
 
   void _remove() {
     _defunct = true;
     _root = null;
+    handleRemoved();
   }
+  void handleRemoved() { }
 
   int _nodeDepth;
   void _ensureDepth() {
     if (_nodeDepth == null) {
       if (_parent != null) {
         _parent._ensureDepth();
         _nodeDepth = _parent._nodeDepth + 1;
       } else {
         _nodeDepth = 0;
       }
@@ skipping 833 matching lines @@
 
 abstract class App extends Component {
   sky.Node _host;
 
   App() : super(stateful: true) {
     _host = sky.document.createElement('div');
     sky.document.appendChild(_host);
     _scheduleComponentForRender(this);
   }
 }