Switch analysis_server to language 2.12, so null safety, but opt-out files.

This should allow doing partial migration, specifically protocol files,
which are imported by other libraries, but are a small library cycle
that does not import much outside of it.

Change-Id: I904c05d6d5b444ee9a9dbd1f7ada12aabdcc5165
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/193583
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

pkg/analysis_server/test/src/plugin/notification_manager_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. 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:analysis_server/protocol/protocol.dart' as server;
 import 'package:analysis_server/protocol/protocol_generated.dart' as server;
 import 'package:analysis_server/src/channel/channel.dart';

pkg/analysis_server/test/src/plugin/plugin_locator_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. 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:analysis_server/src/plugin/plugin_locator.dart';
 import 'package:analyzer/src/test_utilities/resource_provider_mixin.dart';
 import 'package:test/test.dart';

pkg/analysis_server/test/src/plugin/plugin_manager_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. 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:io' as io;
 
 import 'package:analysis_server/src/plugin/notification_manager.dart';

pkg/analysis_server/test/src/plugin/plugin_watcher_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. 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:async';
 
 import 'package:analysis_server/src/plugin/plugin_locator.dart';

pkg/analysis_server/test/src/plugin/protocol_test_utilities.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. 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:analysis_server/protocol/protocol_generated.dart' as server;
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:analyzer_plugin/protocol/protocol_generated.dart' as plugin;

pkg/analysis_server/test/src/plugin/request_converter_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. 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:analysis_server/protocol/protocol_generated.dart' as server;
 import 'package:analysis_server/src/plugin/request_converter.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';

pkg/analysis_server/test/src/plugin/result_collector_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. 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:analysis_server/src/plugin/result_collector.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';

pkg/analysis_server/test/src/plugin/result_converter_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. 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:analysis_server/protocol/protocol_generated.dart' as server;
 import 'package:analysis_server/src/plugin/result_converter.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';

pkg/analysis_server/test/src/plugin/result_merger_test.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. 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:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/plugin/result_merger.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';

pkg/analysis_server/test/src/plugin/test_all.dart

@@ -2,6 +2,8 @@
 // for details. All rights reserved. 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:test_reflective_loader/test_reflective_loader.dart';
 
 import 'notification_manager_test.dart' as notification_manager_test;