Make Sky example game run offline

sky/sdk/example/game/lib/sprites.dart

Index: sky/sdk/example/game/lib/sprites.dart
diff --git a/sky/sdk/example/game/lib/sprites.dart b/sky/sdk/example/game/lib/sprites.dart
index f926906282eae524b96ab2ff70f203a7ac468428..1cd9f905c40e498fefd435cdb6b8799b3513acf8 100644
--- a/sky/sdk/example/game/lib/sprites.dart
+++ b/sky/sdk/example/game/lib/sprites.dart
@@ -1,11 +1,16 @@
+// 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.
+
 library sprites;
 
+import 'dart:async';
 import 'dart:math' as Math;
 import 'dart:sky';
 import 'dart:convert';
 
 import 'package:sky/base/scheduler.dart' as scheduler;
-import 'package:sky/mojo/net/image_cache.dart' as image_cache;
+import 'package:sky/mojo/asset_bundle.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
 import 'package:sky/widgets/widget.dart';