Partial implementation of the 'setAnalysisRoots' API.

pkg/analysis_server/lib/src/protocol.dart

Index: pkg/analysis_server/lib/src/protocol.dart
diff --git a/pkg/analysis_server/lib/src/protocol.dart b/pkg/analysis_server/lib/src/protocol.dart
index 21d8b08b6ae918573d44bb1a92f2e0b003e1ff24..213794134a83d7592ed01e15169da3228fda96ea 100644
--- a/pkg/analysis_server/lib/src/protocol.dart
+++ b/pkg/analysis_server/lib/src/protocol.dart
@@ -462,6 +462,9 @@ class Response {
   Response.contextAlreadyExists(Request request)
     : this(request.id, new RequestError(-8, 'Context already exists'));
 
+  Response.unsupportedFeature(Request request, String message)
+    : this(request.id, new RequestError(-9, message));
+
   /**
    * Initialize a newly created instance based upon the given JSON data
    */
@@ -690,6 +693,9 @@ class RequestError {
     }
     return jsonObject;
   }
+
+  @override
+  String toString() => toJson().toString();
 }
 
 /**