Add a basic popup menu implementation to stocks2

sky/sdk/lib/framework/fn2.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 'app.dart';
 import 'dart:async';
 import 'dart:collection';
 import 'dart:mirrors';
@@ skipping 963 matching lines @@
     if (padding != null)
       current = new Padding(padding: padding, child: current);
 
     if (decoration != null)
       current = new DecoratedBox(decoration: decoration, child: current);
 
     if (desiredSize != null)
       current = new SizedBox(desiredSize: desiredSize, child: current);
 
     if (constraints != null)
-      current = new ConstrainedBox(constraints: constraints);
+      current = new ConstrainedBox(constraints: constraints, child: current);
 
     if (margin != null)
       current = new Padding(padding: margin, child: current);
 
     if (transform != null)
       current = new Transform(transform: transform, child: current);
 
     if (current == null)
       current = new SizedBox();
 
@@ skipping 38 matching lines @@
     assert(root.parent is RenderView);
   }
 }
 
 class Text extends Component {
   Text(this.data) : super(key: '*text*');
   final String data;
   bool get interchangeable => true;
   UINode build() => new Paragraph(text: data);
 }