Drops detached message until we can handle it properly (#45430)

packages/flutter/lib/src/scheduler/binding.dart

@@ -338,6 +338,11 @@ mixin SchedulerBinding on BindingBase, ServicesBinding {
   }
 
   Future<String> _handleLifecycleMessage(String message) async {
+    // TODO(chunhtai): remove the workaround once the issue is fixed
+    // https://github.com/flutter/flutter/issues/39832
+    if (message == 'AppLifecycleState.detached')
+      return null;
+
     handleAppLifecycleStateChanged(_parseAppLifecycleMessage(message));
     return null;
   }

packages/flutter/test/widgets/binding_test.dart

@@ -67,6 +67,14 @@ void main() {
     message = const StringCodec().encodeMessage('AppLifecycleState.inactive');
     await defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { });
     expect(observer.lifecycleState, AppLifecycleState.inactive);
+
+
+    message = const StringCodec().encodeMessage('AppLifecycleState.detached');
+    await defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { });
+    // TODO(chunhtai): this should be detached once the issue is fixed
+    // https://github.com/flutter/flutter/issues/39832
+    // The binding drops detached message for now.
+    expect(observer.lifecycleState, AppLifecycleState.inactive);
   });
 
   testWidgets('didPushRoute callback', (WidgetTester tester) async {