Clean up how we remove nodes from the render tree, and make sure we reinsert them in the right plac…

sky/sdk/lib/widgets/scaffold.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.
 
 import '../rendering/box.dart';
 import '../rendering/object.dart';
 import '../theme2/view_configuration.dart';
 import 'widget.dart';
 
 enum ScaffoldSlots {
@@ skipping 167 matching lines @@
   Widget _drawer;
   Widget _floatingActionButton;
 
   RenderScaffold get root => super.root;
   RenderScaffold createNode() => new RenderScaffold();
 
   void insert(RenderObjectWrapper child, ScaffoldSlots slot) {
     root[slot] = child != null ? child.root : null;
   }
 
-  void removeChild(Widget node) {
-    assert(node != null);
-    root.remove(node.root);
-    super.removeChild(node);
+  void detachChildRoot(RenderObjectWrapper child) {
+    final root = this.root; // TODO(ianh): Remove this once the analyzer is cleverer
+    assert(root is RenderScaffold);
+    assert(root == child.root.parent);
+    root.remove(child.root);
+    assert(root == this.root); // TODO(ianh): Remove this once the analyzer is cleverer
   }
 
   void remove() {
     if (_toolbar != null)
       removeChild(_toolbar);
     if (_body != null)
       removeChild(_body);
     if (_statusBar != null)
       removeChild(_statusBar);
     if (_drawer != null)
       removeChild(_drawer);
     if (_floatingActionButton != null)
       removeChild(_floatingActionButton);
     super.remove();
   }
 
   void syncRenderObject(Widget old) {
     super.syncRenderObject(old);
     _toolbar = syncChild(_toolbar, old is Scaffold ? old._toolbar : null, ScaffoldSlots.toolbar);
     _body = syncChild(_body, old is Scaffold ? old._body : null, ScaffoldSlots.body);
     _statusBar = syncChild(_statusBar, old is Scaffold ? old._statusBar : null, ScaffoldSlots.statusBar);
     _drawer = syncChild(_drawer, old is Scaffold ? old._drawer : null, ScaffoldSlots.drawer);
     _floatingActionButton = syncChild(_floatingActionButton, old is Scaffold ? old._floatingActionButton : null, ScaffoldSlots.floatingActionButton);
   }
 
 }