Make the popup menu width animation work

sky/sdk/lib/widgets/scrollable.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 'dart:sky' as sky;
 
 import 'package:newton/newton.dart';
 import 'package:sky/animation/animated_simulation.dart';
 import 'package:sky/animation/scroll_behavior.dart';
 import 'package:sky/theme/view_configuration.dart' as config;
 import 'package:sky/widgets/basic.dart';
-import 'package:sky/widgets/material.dart';
 
 const double _kMillisecondsPerSecond = 1000.0;
 
 double _velocityForFlingGesture(double eventVelocity) {
   return eventVelocity.clamp(-config.kMaxFlingVelocity, config.kMaxFlingVelocity) /
     _kMillisecondsPerSecond;
 }
 
 abstract class ScrollClient {
   bool ancestorScrolled(Scrollable ancestor);
 }
 
 enum ScrollDirection { vertical, horizontal }
 
 abstract class Scrollable extends StatefulComponent {
 
   Scrollable({
     String key,
-    this.backgroundColor,
     this.direction: ScrollDirection.vertical
   }) : super(key: key);
 
-  Color backgroundColor;
   ScrollDirection direction;
 
   void initState() {
     _animation = new AnimatedSimulation(_tickScrollOffset);
   }
 
   void syncFields(Scrollable source) {
-    backgroundColor = source.backgroundColor;
     direction == source.direction;
   }
 
   double _scrollOffset = 0.0;
   double get scrollOffset => _scrollOffset;
 
   ScrollBehavior _scrollBehavior;
   ScrollBehavior createScrollBehavior();
   ScrollBehavior get scrollBehavior {
     if (_scrollBehavior == null)
       _scrollBehavior = createScrollBehavior();
     return _scrollBehavior;
   }
 
   AnimatedSimulation _animation;
 
   Widget buildContent();
 
   Widget build() {
     return new Listener(
-      child: new Material(
-        type: MaterialType.canvas,
-        child: buildContent(),
-        color: backgroundColor
-      ),
+      child: buildContent(),
       onPointerDown: _handlePointerDown,
       onPointerUp: _handlePointerUpOrCancel,
       onPointerCancel: _handlePointerUpOrCancel,
       onGestureFlingStart: _handleFlingStart,
       onGestureFlingCancel: _handleFlingCancel,
       onGestureScrollUpdate: _handleScrollUpdate,
       onWheel: _handleWheel
     );
   }
 
@@ skipping 88 matching lines @@
 
   void _handleFlingCancel(sky.GestureEvent event) {
     settleScrollOffset();
   }
 
   void _handleWheel(sky.WheelEvent event) {
     scrollBy(-event.offsetY);
   }
 
 }