Opt out of null safety in preparation for min SDK constraint update (#1270)

We are going to update the min SDK constraint in the near future to
a newer SDK version that supports null safety by default. Opt out
of null safety preemptively so subsequent changes contain only
changes relevant to the topic of the issue at hand.

Author: Anna Gringauze

dwds/CHANGELOG.md

@@ -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:build/build.dart';
 
 /// Factory for the build script.

dwds/debug_extension/tool/copy_builder.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
+
 @JS()
 library background;
 

dwds/debug_extension/web/background.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:built_collection/built_collection.dart';
 import 'package:built_value/built_value.dart';
 import 'package:built_value/serializer.dart';

dwds/lib/data/build_result.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:built_value/built_value.dart';
 import 'package:built_value/serializer.dart';
 

dwds/lib/data/build_result.g.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:built_value/built_value.dart';
 import 'package:built_value/serializer.dart';
 

dwds/lib/data/connect_request.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:built_value/built_value.dart';
 import 'package:built_value/serializer.dart';
 

dwds/lib/data/connect_request.g.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:built_collection/built_collection.dart';
 import 'package:built_value/built_value.dart';
 import 'package:built_value/serializer.dart';

dwds/lib/data/devtools_request.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:built_value/built_value.dart';
 import 'package:built_value/serializer.dart';
 

dwds/lib/data/devtools_request.g.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:built_value/built_value.dart';
 import 'package:built_value/serializer.dart';
 

dwds/lib/data/error_response.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:built_collection/built_collection.dart';
 import 'package:built_value/serializer.dart';
 

dwds/lib/data/error_response.g.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:logging/logging.dart';

dwds/lib/data/extension_request.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 'dart:convert';
 

dwds/lib/data/extension_request.g.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:vm_service/vm_service.dart';

dwds/lib/data/isolate_events.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.import 'dart:async';
 
+// @dart = 2.9
+
 import 'package:vm_service/vm_service.dart';
 import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart';
 

dwds/lib/data/isolate_events.g.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:webkit_inspection_protocol/webkit_inspection_protocol.dart';
 
 import '../utilities/objects.dart';

dwds/lib/data/run_request.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 'dart:math' as math;
 

dwds/lib/data/run_request.g.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:async/async.dart';

dwds/lib/data/serializers.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:pool/pool.dart';
 import 'package:vm_service/vm_service.dart';
 import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart';

dwds/lib/data/serializers.g.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.import 'dart:async';
 
+// @dart = 2.9
+
 import 'package:path/path.dart' as p;
 import 'package:vm_service/vm_service.dart';
 import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart';

dwds/lib/dwds.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:math';
 
 import 'package:vm_service/vm_service.dart';

dwds/lib/src/connections/app_connection.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.import 'dart:async';
 
+// @dart = 2.9
+
 import 'package:vm_service/vm_service.dart';
 
 import '../loaders/strategy.dart';

dwds/lib/src/connections/debug_connection.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:path/path.dart' as p;
 import 'package:source_maps/parser.dart';
 import 'package:source_maps/source_maps.dart';

dwds/lib/src/debugging/classes.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.import 'dart:async';
 
+// @dart = 2.9
+
 import 'package:vm_service/vm_service.dart';
 import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart';
 

dwds/lib/src/debugging/dart_scope.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.import 'dart:async';
 
+// @dart = 2.9
+
 import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart';
 
 import '../../loaders/strategy.dart';

dwds/lib/src/debugging/debugger.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
+
 /// Module metadata format version
 ///
 /// Module reader always creates the current version but is able to read

dwds/lib/src/debugging/execution_context.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.import 'dart:async';
 
+// @dart = 2.9
+
 import 'dart:async';
 import 'dart:convert';
 

dwds/lib/src/debugging/frame_computer.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:async/async.dart';
 
 import '../loaders/strategy.dart';

dwds/lib/src/debugging/inspector.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:webkit_inspection_protocol/webkit_inspection_protocol.dart';
 
 /// A generic debugger used in remote debugging.

dwds/lib/src/debugging/instance.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 'location.dart';
 
 const maxValue = 2147483647;

dwds/lib/src/debugging/libraries.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:webkit_inspection_protocol/webkit_inspection_protocol.dart';
 
 import 'remote_debugger.dart';

dwds/lib/src/debugging/location.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 'dart:convert';
 

dwds/lib/src/debugging/metadata/class.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';
 
 class DwdsEvent {

dwds/lib/src/debugging/metadata/function.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 'dart:convert';
 import 'dart:io';

dwds/lib/src/debugging/metadata/module_metadata.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 'dart:convert';
 import 'dart:io';

dwds/lib/src/debugging/metadata/provider.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:async/async.dart';