[Effen] Add a basic layout test

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 436 matching lines @@
 
       _class = styles.map((s) => s._className).join(' ');
     }
   }
 
   void _syncNode(RenderNode old) {
     Element oldElement = old as Element;
     sky.Element root = _root as sky.Element;
 
     _ensureClass();
-    if (_class != oldElement._class)
+    if (_class != oldElement._class && _class != '')
       root.setAttribute('class', _class);
 
     if (inlineStyle != oldElement.inlineStyle)
       root.setAttribute('style', inlineStyle);
 
     _syncChildren(oldElement);
   }
 
   void _syncChildren(Element oldElement) {
     sky.Element root = _root as sky.Element;
@@ skipping 431 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);
   }
 }