Make it possible to test that the stock app doesn't crash on startup and...

Make it possible to test that the stock app doesn't crash on startup and paints the basic scaffold more or less correctly.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/1177043008.

examples/stocks2/lib/stock_app.dart

@@ -2,7 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:sky/framework/app.dart';
 import 'package:sky/framework/editing2/input.dart';
+import 'package:sky/framework/rendering/box.dart';
 import 'package:sky/framework/theme2/colors.dart' as colors;
 import 'package:sky/framework/widgets/drawer.dart';
 import 'package:sky/framework/widgets/drawer_header.dart';
@@ -32,7 +34,7 @@ class StocksApp extends App {
 
   List<Stock> _stocks = [];
 
-  StocksApp() : super() {
+  StocksApp({ RenderView renderViewOverride }) : super(renderViewOverride: renderViewOverride) {
     // if (debug)
     //   new Timer(new Duration(seconds: 1), dumpState);
     new StockDataFetcher((StockData data) {