Refactor fn2.dart, since it breached our 1000-line threshold.

sky/examples/stocks2/lib/stock_list.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 'package:sky/framework/components2/fixed_height_scrollable.dart';
-import 'package:sky/framework/fn2.dart';
+import 'package:sky/framework/widgets/fixed_height_scrollable.dart';
+import 'package:sky/framework/widgets/wrappers.dart';
+
 import 'stock_data.dart';
 import 'stock_row.dart';
 
 class Stocklist extends FixedHeightScrollable {
 
   Stocklist({
     Object key,
     this.stocks,
     this.query
   }) : super(itemHeight: StockRow.kHeight, key: key);
@@ skipping 13 matching lines @@
              stock.symbol.contains(new RegExp(query, caseSensitive: false));
     });
     itemCount = filteredStocks.length;
     return filteredStocks
       .skip(start)
       .take(count)
       .map((stock) => new StockRow(stock: stock))
       .toList(growable: false);
   }
 }