[Effen] fix some dart warnings (mostly unused imports)

sky/framework/components/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 'animated_component.dart';
 import '../animation/animated_value.dart';
 import '../fn.dart';
 import '../theme/colors.dart';
-import '../theme/view-configuration.dart';
 import 'dart:async';
 import 'dart:math' as math;
-import 'dart:sky' as sky;
 import 'material.dart';
 import 'popup_menu_item.dart';
 
 const double _kMenuOpenDuration = 300.0;
 const double _kMenuCloseDuration = 200.0;
 const double _kMenuCloseDelay = 100.0;
 
 enum MenuState { Hidden, Opening, Open, Closing }
 
 class PopupMenuController {
@@ skipping 14 matching lines @@
   Future _closeState;
   close() async {
     var result = new Completer();
     _closeState = result.future;
     if ((_state == MenuState.Opening) || (_state == MenuState.Open)) {
       _state = MenuState.Closing;
       await position.animateTo(0.0, _kMenuCloseDuration, initialDelay: _kMenuCloseDelay);
       _state = MenuState.Hidden;
       _closeState = null;
       result.complete();
-      return;
+      return result.future;
     }
     assert(_closeState != null);
     return _closeState;
   }
 }
 
 class PopupMenu extends AnimatedComponent {
   static final Style _style = new Style('''
     border-radius: 2px;
     padding: 8px 0;
@@ skipping 50 matching lines @@
 
     return new Material(
       content: new Container(
         style: _style,
         inlineStyle: _inlineStyle(),
         children: children
       ),
       level: level);
   }
 }