Add material shadows to toolbar and drawer

sky/sdk/lib/framework/components2/fixed_height_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 '../animation/scroll_behavior.dart';
 import '../fn2.dart';
 import 'dart:async';
 import 'dart:math' as math;
 import 'package:vector_math/vector_math.dart';
 import 'scrollable.dart';
@@ skipping 45 matching lines @@
         double drawStart = scrollOffset + alignmentDelta;
         itemNumber = math.max(0, (drawStart / itemHeight).floor());
 
         transform.translate(0.0, alignmentDelta);
       }
     }
 
     return new SizeObserver(
       callback: _handleSizeChanged,
       child: new Clip(
-        child: new Transform(
-          transform: transform,
-          child: new BlockContainer(
-            children: buildItems(itemNumber, itemCount))
+        child: new DecoratedBox(
+          decoration: const BoxDecoration(
+            backgroundColor: const Color(0xFFFFFFFF)
+          ),
+          child: new Transform(
+            transform: transform,
+            child: new BlockContainer(
+              children: buildItems(itemNumber, itemCount))
+          )
         )
       )
     );
   }
 
   List<UINode> buildItems(int start, int count);  
 }