Make it possible to construct a Stock directly

sky/examples/stocks-fn/lib/stock_data.dart

Index: sky/examples/stocks-fn/lib/stock_data.dart
diff --git a/sky/examples/stocks-fn/lib/stock_data.dart b/sky/examples/stocks-fn/lib/stock_data.dart
index 9ca0de86ff134deaa48a762a50c5de778d6bc672..17e083c1cc3112e87fbfb22c1750127aeacef57b 100644
--- a/sky/examples/stocks-fn/lib/stock_data.dart
+++ b/sky/examples/stocks-fn/lib/stock_data.dart
@@ -23,7 +23,7 @@ class Stock {
   String marketCap;
   double percentChange;
 
-  Stock(this.symbol, this.name, this.lastSale, this.marketCap);
+  Stock(this.symbol, this.name, this.lastSale, this.marketCap, this.percentChange);
 
   Stock.fromFields(List<String> fields) {
     // FIXME: This class should only have static data, not lastSale, etc.