Remove one more use of mirrors: Components now have to explicitly sync their fields.

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';
 
 abstract class FixedHeightScrollable extends Scrollable {
+
   FixedHeightScrollable({ this.itemHeight, Object key }) : super(key: key) {
     assert(itemHeight != null);
   }
 
+  double itemHeight;
+
+  void syncFields(FixedHeightScrollable source) {
+    itemHeight = source.itemHeight;
+    super.syncFields(source);
+  }
+
   ScrollBehavior createScrollBehavior() => new OverscrollBehavior();
   OverscrollBehavior get scrollBehavior => super.scrollBehavior as OverscrollBehavior;
 
-  double _height;
-  final double itemHeight;
-
   int _itemCount = 0;
   int get itemCount => _itemCount;
   void set itemCount (int value) {
     if (_itemCount != value) {
       _itemCount = value;
       scrollBehavior.contentsHeight = itemHeight * _itemCount;
     }
   }
 
+  double _height;
   void _handleSizeChanged(Size newSize) {
     setState(() {
       _height = newSize.height;
       scrollBehavior.containerHeight = _height;
     });
   }
 
   UINode buildContent() {
-    var itemNumber = 0;
-    var itemCount = 0;
+    var itemShowIndex = 0;
+    var itemShowCount = 0;
 
     Matrix4 transform = new Matrix4.identity();
 
     if (_height != null && _height > 0.0) {
       if (scrollOffset < 0.0) {
         double visibleHeight = _height + scrollOffset;
-        itemCount = (visibleHeight / itemHeight).round() + 1;
+        itemShowCount = (visibleHeight / itemHeight).round() + 1;
         transform.translate(0.0, -scrollOffset);
       } else {
-        itemCount = (_height / itemHeight).ceil() + 1;
+        itemShowCount = (_height / itemHeight).ceil() + 1;
         double alignmentDelta = -scrollOffset % itemHeight;
         if (alignmentDelta != 0.0)
           alignmentDelta -= itemHeight;
 
         double drawStart = scrollOffset + alignmentDelta;
-        itemNumber = math.max(0, (drawStart / itemHeight).floor());
+        itemShowIndex = math.max(0, (drawStart / itemHeight).floor());
 
         transform.translate(0.0, alignmentDelta);
       }
     }
 
     return new SizeObserver(
       callback: _handleSizeChanged,
       child: new Clip(
         child: new DecoratedBox(
           decoration: const BoxDecoration(
             backgroundColor: const Color(0xFFFFFFFF)
           ),
           child: new Transform(
             transform: transform,
             child: new BlockContainer(
-              children: buildItems(itemNumber, itemCount))
+              children: buildItems(itemShowIndex, itemShowCount))
           )
         )
       )
     );
   }
 
   List<UINode> buildItems(int start, int count);  
+
 }