In the analysis server API, change RequestError.code to an enum.

pkg/analysis_server/test/analysis/get_errors_test.dart

Index: pkg/analysis_server/test/analysis/get_errors_test.dart
diff --git a/pkg/analysis_server/test/analysis/get_errors_test.dart b/pkg/analysis_server/test/analysis/get_errors_test.dart
index cc9224c883a99444e607a6e2cc66ae32d40f6e0c..a3da0b3df6bea5ff9524081423ef7fd1e7d773fe 100644
--- a/pkg/analysis_server/test/analysis/get_errors_test.dart
+++ b/pkg/analysis_server/test/analysis/get_errors_test.dart
@@ -113,7 +113,7 @@ main() {
       expect(result.errors, isEmpty);
       RequestError error = response.error;
       expect(error, isNotNull);
-      expect(error.code, 'GET_ERRORS_ERROR');
+      expect(error.code, RequestErrorCode.GET_ERRORS_ERROR);
     });
   }