Created Dart Debug Extension request & response. (#499)

* Created extension request & response.

Author: Pi Songkuntham

dwds/lib/data/extension_request.dart

@@ -0,0 +1,51 @@
+// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
+// 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 'package:built_collection/built_collection.dart';
+import 'package:built_value/built_value.dart';
+import 'package:built_value/serializer.dart';
+
+part 'extension_request.g.dart';
+
+/// A request to run a command in the Dart Debug Extension.
+abstract class ExtensionRequest
+    implements Built<ExtensionRequest, ExtensionRequestBuilder> {
+  static Serializer<ExtensionRequest> get serializer =>
+      _$extensionRequestSerializer;
+
+  factory ExtensionRequest([Function(ExtensionRequestBuilder) updates]) =
+      _$ExtensionRequest;
+
+  ExtensionRequest._();
+
+  /// Used to associate a request with an [ExtensionResponse].
+  int get id;
+
+  String get command;
+
+  BuiltMap<String, Object> get commandParams;
+}
+
+/// A response to an [ExtensionRequest].
+abstract class ExtensionResponse
+    implements Built<ExtensionResponse, ExtensionResponseBuilder> {
+  static Serializer<ExtensionResponse> get serializer =>
+      _$extensionResponseSerializer;
+
+  factory ExtensionResponse([Function(ExtensionResponseBuilder) updates]) =
+      _$ExtensionResponse;
+
+  ExtensionResponse._();
+
+  /// Used to associate a response with an [ExtensionRequest].
+  int get id;
+
+  bool get success;
+
+  /// Contains a JSON-encoded payload.
+  String get result;
+
+  @nullable
+  String get error;
+}