Use HasToJson when set Reponse/Notification parameters.

pkg/analysis_server/lib/src/collections.dart

Index: pkg/analysis_server/lib/src/collections.dart
diff --git a/pkg/analysis_server/lib/src/collections.dart b/pkg/analysis_server/lib/src/collections.dart
new file mode 100644
index 0000000000000000000000000000000000000000..6049add34e0f0a175f41b2e7c7aeb389267c6481
--- /dev/null
+++ b/pkg/analysis_server/lib/src/collections.dart
@@ -0,0 +1,16 @@
+// Copyright (c) 2014, 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.
+
+library collections;
+
+/**
+ * Instances of the class [HasToJson] implement [toJson] method that returns
+ * a JSON presentation.
+ */
+abstract class HasToJson {
+  /**
+   * Returns a JSON presentation of the object.
+   */
+  Map<String, Object> toJson();
+}