fix minedigger win bug

sky/examples/mine_digger/mine_digger.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 'dart:sky' as sky;
 import 'dart:math';
 
 import 'package:sky/rendering/flex.dart';
 import 'package:sky/widgets/basic.dart';
 import 'package:sky/widgets/scaffold.dart';
@@ skipping 153 matching lines @@
     return new ToolBar(
       // FIXME: Strange to have the toolbar be tapable.
       center: new Listener(
         onPointerDown: handleBannerPointerDown,
         child: new Text(banner, style: Theme.of(this.app).text.title)
       )
     );
   }
 
   Widget buildUI() {
+    // FIXME: We need to build the board before we build the toolbar because
+    // we compute the win state during build step.
+    Widget board = buildBoard();
     return new Scaffold(
       toolbar: buildToolBar(),
       body: new Container(
-        child: new Center(child: buildBoard()),
+        child: new Center(child: board),
         decoration: new BoxDecoration(backgroundColor: colors.Grey[50])
       )
     );
   }
 
   void handleBannerPointerDown(sky.PointerEvent event) {
     initialize();
     app.setState((){});
   }
 
@@ skipping 173 matching lines @@
   }
 
   Widget build() {
     return game.buildUI();
   }
 }
 
 void main() {
   runApp(new MineDiggerApp());
 }