Set language to 2.15 for frontend_server, opt-out all existing files.

I will add new functionality (binary protocol for macro compilation),
and would like to use modern language version.

Change-Id: I2fc0dc57b64b41669e76a81dff76b0eac93808e5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/239621
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

.dart_tool/package_config.json

@@ -326,7 +326,7 @@
       "name": "frontend_server",
       "rootUri": "../pkg/frontend_server",
       "packageUri": "lib/",
-      "languageVersion": "2.7"
+      "languageVersion": "2.15"
     },
     {
       "name": "frontend_server_client",

pkg/frontend_server/bin/frontend_server_starter.dart

@@ -1,3 +1,4 @@
+// @dart = 2.9
 library frontend_server;
 
 import 'dart:async';

pkg/frontend_server/lib/frontend_server.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 library frontend_server;
 
 import 'dart:async';

pkg/frontend_server/lib/src/javascript_bundle.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'dart:convert';
 import 'dart:io';
 

pkg/frontend_server/lib/src/strong_components.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'package:kernel/ast.dart';
 import 'package:kernel/util/graph.dart';
 

pkg/frontend_server/pubspec.yaml

@@ -4,7 +4,7 @@ description: A resident kernel compiler
 publish_to: none
 
 environment:
-  sdk: "^2.7.0"
+  sdk: "^2.15.0"
 
 dependencies:
   args: ^2.0.0

pkg/frontend_server/test/frontend_server_flutter.dart

@@ -1,3 +1,4 @@
+// @dart = 2.9
 import 'dart:async' show StreamController;
 import 'dart:convert' show utf8, LineSplitter;
 import 'dart:io' show Directory, File, FileSystemEntity, IOSink, exitCode;

pkg/frontend_server/test/frontend_server_flutter_suite.dart

@@ -2,6 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
+// @dart = 2.9
 import 'dart:async' show StreamSubscription, Timer;
 import 'dart:convert' show jsonEncode;
 import 'dart:io' show File, exitCode;

pkg/frontend_server/test/frontend_server_test.dart

@@ -1,3 +1,4 @@
+// @dart = 2.9
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';

pkg/frontend_server/test/src/javascript_bundle_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'dart:convert';
 import 'dart:io';
 

pkg/frontend_server/test/src/strong_components_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.9
 import 'package:frontend_server/src/strong_components.dart';
 import 'package:kernel/ast.dart';
 import 'package:test/test.dart';