Split layout2.dart into several files

sky/sdk/lib/framework/components2/drawer_header.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 '../fn2.dart';
-import '../layout2.dart';
 import '../theme/colors.dart';
 import '../theme/view_configuration.dart';
 
 class DrawerHeader extends Component {
   static final Style _style = new Style('''
     height: ${140 + kStatusBarHeight}px;
     background-color: ${BlueGrey[50]};
     border-bottom: 1px solid #D1D9E1;
     padding-bottom: 7px;
     margin-bottom: 8px;'''
@@ skipping 20 matching lines @@
         ),
         new Container(
           key: 'Label',
           style: _labelStyle,
           children: children
         )
       ]
     );
   }
 }