Make it harder to forget itemCount for FixedHeightScrollable

sky/sdk/example/stocks/lib/stock_list.dart

Index: sky/sdk/example/stocks/lib/stock_list.dart
diff --git a/sky/sdk/example/stocks/lib/stock_list.dart b/sky/sdk/example/stocks/lib/stock_list.dart
index 4b36783d186d25f5a0cd5920b5794a8a234cc844..38255540c760ed9ea070f1dc60ed226d93799a7c 100644
--- a/sky/sdk/example/stocks/lib/stock_list.dart
+++ b/sky/sdk/example/stocks/lib/stock_list.dart
@@ -12,25 +12,31 @@ class Stocklist extends FixedHeightScrollable {
 
   Stocklist({
     String key,
-    this.stocks,
+    List<Stock> stocks,
     this.query

[Hixie, 2015/07/07 15:25:13]

do we still need to remember the query?

[abarth-chromium, 2015/07/07 15:26:21]

Nope!

-  }) : super(itemHeight: StockRow.kHeight, key: key);
+  }) : super(itemHeight: StockRow.kHeight, key: key) {
+    if (query == null) {
+      filteredStocks = stocks;
+    } else {
+      RegExp regexp = new RegExp(query, caseSensitive: false);
+      filteredStocks = stocks
+        .where((stock) => stock.symbol.contains(regexp))
+        .toList(growable: false);
+    }
+  }
 
   String query;
-  List<Stock> stocks;
+  List<Stock> filteredStocks;
+
+  int get itemCount => filteredStocks.length;
 
   void syncFields(Stocklist source) {
     query = source.query;
-    stocks = source.stocks;
+    filteredStocks = source.filteredStocks;
     super.syncFields(source);
   }
 
   List<Widget> buildItems(int start, int count) {
-    var filteredStocks = stocks.where((stock) {
-      return query == null ||
-             stock.symbol.contains(new RegExp(query, caseSensitive: false));
-    });
-    itemCount = filteredStocks.length;
     return filteredStocks
       .skip(start)
       .take(count)