Upgrading samples to flutter_lints, part 1 of n (#804)

platform_channels/test/src/add_pet_details_test.dart

@@ -12,7 +12,8 @@ void main() {
     var petList = <Map>[];
 
     setUpAll(() {
-      BasicMessageChannel<dynamic>('jsonMessageCodecDemo', JSONMessageCodec())
+      const BasicMessageChannel<dynamic>(
+              'jsonMessageCodecDemo', JSONMessageCodec())
           .setMockMessageHandler((dynamic message) async {
         petList.add(message as Map);
       });

platform_channels/test/src/method_channel_demo_test.dart

@@ -10,7 +10,7 @@ import 'package:platform_channels/src/method_channel_demo.dart';
 void main() {
   group('MethodChannelDemo tests', () {
     setUpAll(() {
-      final methodChannel = MethodChannel('methodChannelDemo');
+      const methodChannel = MethodChannel('methodChannelDemo');
 
       // Register a mock MethodCallHandler.
       methodChannel.setMockMethodCallHandler((call) async {

platform_channels/test/src/pet_list_screen_test.dart

@@ -12,7 +12,7 @@ import 'package:platform_channels/src/pet_list_screen.dart';
 
 void main() {
   group('PetListScreen tests', () {
-    final basicMessageChannel =
+    const basicMessageChannel =
         BasicMessageChannel('stringCodecDemo', StringCodec());
 
     var petList = [
@@ -33,7 +33,7 @@ void main() {
 
       // Mock for the index received from the Dart to delete the pet details,
       // and send the updated pet list back to Dart.
-      BasicMessageChannel('binaryCodecDemo', BinaryCodec())
+      const BasicMessageChannel('binaryCodecDemo', BinaryCodec())
           .setMockMessageHandler((message) async {
         // Convert the ByteData to String.
         final index = utf8.decoder.convert(message.buffer

platform_channels/test/src/platform_image_demo_test.dart

@@ -11,7 +11,8 @@ void main() {
   group('Platform Image Demo tests', () {
     setUpAll(() {
       // Register a mock for MessageHandler.
-      BasicMessageChannel<dynamic>('platformImageDemo', StandardMessageCodec())
+      const BasicMessageChannel<dynamic>(
+              'platformImageDemo', StandardMessageCodec())
           .setMockMessageHandler((dynamic message) async {
         var byteData = await rootBundle.load('assets/eat_new_orleans.jpg');
         return byteData.buffer.asUint8List();