Make it possible to detect PopupMenuItem presses

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 'package:sky/painting/text_style.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/default_text_style.dart';
 import 'package:sky/widgets/ink_well.dart';
 import 'package:sky/widgets/theme.dart';
 
 const double kMenuItemHeight = 48.0;
 const double kBaselineOffsetFromBottom = 20.0;
 
 class PopupMenuItem extends Component {
-  PopupMenuItem({ String key, this.child, this.opacity}) : super(key: key);
+  PopupMenuItem({
+    String key,
+    this.onPressed,
+    this.child
+  }) : super(key: key);
 
   final Widget child;
-  final double opacity;
+  final Function onPressed;
 
   TextStyle get textStyle => Theme.of(this).text.subhead;
 
   Widget build() {
-    return new Opacity(
-      opacity: opacity,
+    return new Listener(
+      onGestureTap: (_) {
+        if (onPressed != null)
+          onPressed();
+      },
       child: new InkWell(
         child: new Container(
           height: kMenuItemHeight,
           child: new DefaultTextStyle(
             style: textStyle,
             child: new Baseline(
               baseline: kMenuItemHeight - kBaselineOffsetFromBottom,
               child: child
             )
           )
         )
       )
     );
   }
 }