Give the popup menu a 2px border radius

sky/sdk/lib/framework/components2/popup_menu.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/animated_value.dart';
 import '../fn2.dart';
 import '../theme2/colors.dart';
 import '../theme2/shadows.dart';
 import 'animated_component.dart';
 import 'dart:async';
@@ skipping 81 matching lines @@
   //   });
   // }
 
   UINode build() {
     int i = 0;
     List<UINode> children = new List.from(items.map((List<UINode> item) {
       double opacity = _opacityFor(i);
       return new PopupMenuItem(key: i++, children: item, opacity: opacity);
     }));
 
-    // border-radius: 2px
     // inlineStyle: _inlineStyle(),
     return new ShrinkWrapWidth(
       child: new Container(
         padding: const EdgeDims.all(8.0),
         decoration: new BoxDecoration(
           backgroundColor: Grey[50],
+          borderRadius: 2.0,
           boxShadow: Shadow[level]),
         child: new BlockContainer(children: children)
       )
     );
   }
 }