Move example fn widgets into sky/framework/components

sky/framework/components/drawer_header.dart

-part of widgets;
+// 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 '../fn.dart';
+import '../theme/colors.dart';
 
 class DrawerHeader extends Component {
-
-  static Style _style = new Style('''
+  static final Style _style = new Style('''
     display: flex;
     flex-direction: column;
     height: 140px;
     -webkit-user-select: none;
     background-color: ${BlueGrey[50]};
     border-bottom: 1px solid #D1D9E1;
     padding-bottom: 7px;
     margin-bottom: 8px;'''
   );
 
-  static Style _spacerStyle = new Style('''
+  static final Style _spacerStyle = new Style('''
     flex: 1'''
   );
 
-  static Style _labelStyle = new Style('''
+  static final Style _labelStyle = new Style('''
     padding: 0 16px;
     font-family: 'Roboto Medium', 'Helvetica';
     color: #212121;'''
   );
 
   List<Node> children;
 
   DrawerHeader({ Object key, this.children }) : super(key: key);
 
   Node build() {
     return new Container(
       style: _style,
       children: [
         new Container(
           key: 'Spacer',
           style: _spacerStyle
         ),
         new Container(
           key: 'Label',
           style: _labelStyle,
           children: children
         )
       ]
     );
   }
 }