Allow Effen Styles to be extendable

sky/framework/components/drawer.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 '../animation/animation.dart';
 import '../animation/curves.dart';
 import '../fn.dart';
 import '../theme/colors.dart';
 import '../theme/shadows.dart';
 import 'dart:async';
@@ skipping 132 matching lines @@
   Node build() {
     _ensureListening();
 
     bool isClosed = _position <= -_kWidth;
     String inlineStyle = 'display: ${isClosed ? 'none' : ''}';
     String maskInlineStyle = 'opacity: ${(_position / _kWidth + 1) * 0.25}';
     String contentInlineStyle = 'transform: translateX(${_position}px)';
 
     Container mask = new Container(
       key: 'Mask',
-      styles: [_maskStyle],
+      style: _maskStyle,
       inlineStyle: maskInlineStyle
     )..events.listen('gesturetap', animation.handleMaskTap)
      ..events.listen('gestureflingstart', animation.handleFlingStart);
 
     Material content = new Material(
       key: 'Content',
-      styles: [_contentStyle],
+      style: _contentStyle,
       inlineStyle: contentInlineStyle,
       children: children,
       level: level
     );
 
     return new Container(
-      styles: [_style],
+      style: _style,
       inlineStyle: inlineStyle,
       children: [ mask, content ]
     );
   }
 }