Use HasToJson when set Reponse/Notification parameters.

pkg/analysis_server/lib/src/search/search_result.dart

Index: pkg/analysis_server/lib/src/search/search_result.dart
diff --git a/pkg/analysis_server/lib/src/search/search_result.dart b/pkg/analysis_server/lib/src/search/search_result.dart
index e9eceedb3edd71e0d754ec2c27897ad227ec5b52..cc366d052dbc3d427d81ce4e502890e2a863151e 100644
--- a/pkg/analysis_server/lib/src/search/search_result.dart
+++ b/pkg/analysis_server/lib/src/search/search_result.dart
@@ -4,6 +4,7 @@
 
 library search.search_result;
 
+import 'package:analysis_server/src/collections.dart';
 import 'package:analysis_server/src/computer/element.dart';
 import 'package:analysis_server/src/constants.dart';
 import 'package:analysis_services/search/search_engine.dart';
@@ -13,7 +14,7 @@ import 'package:analyzer/src/generated/element.dart' as engine;
 /**
  * A single result from a search request.
  */
-class SearchResult {
+class SearchResult implements HasToJson {
   /**
    * The kind of element that was found or the kind of reference that was found.
    */