Fix test failures from my previous animation patch.

sky/sdk/lib/widgets/material.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 '../base/lerp.dart';
 import '../animation/animated_value.dart';
 import '../painting/box_painter.dart';
 import '../theme/edges.dart';
 import '../theme/shadows.dart';
 import 'animated_component.dart';
@@ skipping 21 matching lines @@
 
 class Material extends AnimatedComponent {
 
   Material({
     String key,
     this.child,
     this.edge: MaterialEdge.card,
     int level: 0,
     this.color
   }) : super(key: key) {
-    this.level = new AnimatedValue(level.toDouble());
+    this.level = new AnimatedValue(level == null ? 0.0 : level.toDouble());
     watch(this.level);
   }
 
   Widget child;
   MaterialEdge edge;
   AnimatedValue level;
   Color color;
 
   void syncFields(Material source) {
     child = source.child;
@@ skipping 14 matching lines @@
         boxShadow: _computeShadow(level.value),
         borderRadius: edges[edge],
         backgroundColor: color,
         shape: edge == MaterialEdge.circle ? Shape.circle : Shape.rectangle
       ),
       child: new DefaultTextStyle(style: Theme.of(this).text.body1, child: child)
     );
   }
 
 }