[Effen] Prevent scrolling past the bottom of a scrollable list.

sky/examples/stocks/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/animation/scroll_behavior.dart';
 import 'package:sky/framework/components/fixed_height_scrollable.dart';
 import 'package:sky/framework/fn.dart';
 import 'stock_data.dart';
 import 'stock_row.dart';
 
 class Stocklist extends FixedHeightScrollable {
   String query;
   List<Stock> stocks;
 
   Stocklist({
     Object key,
     this.stocks,
     this.query
-  }) : super(key: key, scrollBehavior: new OverscrollBehavior());
+  }) : super(key: key);
 
   List<UINode> buildItems(int start, int count) {
-    return stocks
-      .where((stock) => query == null || stock.symbol.contains(
-          new RegExp(query, caseSensitive: false)))
+    var filteredStocks = stocks.where((stock) {
+      return query == null ||
+             stock.symbol.contains(new RegExp(query, caseSensitive: false));
+    });
+    itemCount = filteredStocks.length;

[abarth-chromium, 2015/06/04 16:23:17]

Won't this |length| query force the filter to be eagerly evaluated on the entire
list?  What if the list of stocks is very, very long?  Previously, this code
only needed to touch enough of the list to get the information visible in the
viewport.

+    return filteredStocks
       .skip(start)
       .take(count)
       .map((stock) => new StockRow(stock: stock))
       .toList(growable: false);
   }
 }