Minor cleanup of error reporting in plugins

pkg/analyzer_plugin/lib/plugin/plugin.dart

Index: pkg/analyzer_plugin/lib/plugin/plugin.dart
diff --git a/pkg/analyzer_plugin/lib/plugin/plugin.dart b/pkg/analyzer_plugin/lib/plugin/plugin.dart
index 0eb38abff5491b2b6b58c6193bf3239a93e44fd8..a10afbb86be648b64fc1ba1bf75960c0e83ba082 100644
--- a/pkg/analyzer_plugin/lib/plugin/plugin.dart
+++ b/pkg/analyzer_plugin/lib/plugin/plugin.dart
@@ -515,7 +515,7 @@ abstract class ServerPlugin {
     }
     if (result == null) {
       return new Response(request.id,
-          error: RequestErrorFactory.unknownRequest(request));
+          error: RequestErrorFactory.unknownRequest(request.method));
     }
     return result.toResponse(request.id);
   }