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

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 'animated_component.dart';
 import '../animation/animated_value.dart';
 import '../animation/curves.dart';
 import '../fn.dart';
 import '../theme/colors.dart';
-import '../theme/shadows.dart';
-import 'dart:async';
 import 'dart:math' as math;
 import 'dart:sky' as sky;
 import 'material.dart';
 
 const double _kWidth = 304.0;
 const double _kMinFlingVelocity = 0.4;
 const double _kBaseSettleDurationMS = 246.0;
 const double _kMaxSettleDurationMS = 600.0;
 const Curve _kAnimationCurve = parabolicRise;
 
@@ skipping 125 matching lines @@
         inlineStyle: inlineStyle,
         children: [ mask, content ]
       ),
       onPointerDown: controller.handlePointerDown,
       onPointerMove: controller.handlePointerMove,
       onPointerUp: controller.handlePointerUp,
       onPointerCancel: controller.handlePointerCancel
     );
   }
 }