Improve the padding and sizing of popup menus.

sky/sdk/lib/widgets/popup_menu_item.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 '../painting/text_style.dart';
 import 'basic.dart';
 import 'default_text_style.dart';
 import 'ink_well.dart';
 import 'theme.dart';
 
 class PopupMenuItem extends Component {
   PopupMenuItem({ String key, this.child, this.opacity}) : super(key: key);
 
   final Widget child;
   final double opacity;
 
   TextStyle get textStyle => Theme.of(this).text.subhead;
 
   Widget build() {
     return new Opacity(
       opacity: opacity,
       child: new InkWell(
         child: new Container(
-          constraints: const BoxConstraints(minWidth: 112.0),
-          padding: const EdgeDims.all(16.0),
+          height: 48.0,
           child: new DefaultTextStyle(
             style: textStyle,
             child: child
           )
         )
       )
     );
   }
 }