refactor: alien sandbox traceable

packages/pinball_components/sandbox/lib/stories/alien_bumper/alien_bumper_game.dart

@@ -5,10 +5,8 @@ import 'package:pinball_components/pinball_components.dart';
 import 'package:sandbox/common/common.dart';
 import 'package:sandbox/stories/ball/basic_ball_game.dart';
 
-class AlienBumperGame extends BasicBallGame {
-  AlienBumperGame({
-    required this.trace,
-  }) : super(color: const Color(0xFF0000FF));
+class AlienBumperGame extends BasicBallGame with Traceable {
+  AlienBumperGame() : super(color: const Color(0xFF0000FF));
 
   static const info = '''
     Shows how a AlienBumper is rendered.
@@ -16,8 +14,6 @@ class AlienBumperGame extends BasicBallGame {
     Activate the "trace" parameter to overlay the body.
 ''';
 
-  final bool trace;
-
   @override
   Future<void> onLoad() async {
     await super.onLoad();
@@ -34,9 +30,6 @@ class AlienBumperGame extends BasicBallGame {
       alienBumperB,
     ]);
 
-    if (trace) {
-      alienBumperA.trace();
-      alienBumperB.trace();
-    }
+    await traceAllBodies();
   }
 }

packages/pinball_components/sandbox/lib/stories/alien_bumper/stories.dart

@@ -7,9 +7,7 @@ void addAlienBumperStories(Dashbook dashbook) {
   dashbook.storiesOf('Alien Bumpers').add(
         'Basic',
         (context) => GameWidget(
-          game: AlienBumperGame(
-            trace: context.boolProperty('Trace', true),
-          ),
+          game: AlienBumperGame()..trace = context.boolProperty('Trace', true),
         ),
         codeLink: buildSourceLink('alien_bumper/basic.dart'),
         info: AlienBumperGame.info,