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

pkg/analysis_server/test/integration/protocol_matchers.dart

Index: pkg/analysis_server/test/integration/protocol_matchers.dart
diff --git a/pkg/analysis_server/test/integration/protocol_matchers.dart b/pkg/analysis_server/test/integration/protocol_matchers.dart
index e493623979b79071dc9fecdb1b342d8dd95be58b..2f10f09a3599be6063a51ac4eaf9b8da6ca16ce1 100644
--- a/pkg/analysis_server/test/integration/protocol_matchers.dart
+++ b/pkg/analysis_server/test/integration/protocol_matchers.dart
@@ -1081,14 +1081,14 @@ final Matcher isElementKind = new MatchesEnum("ElementKind", [
  * Error
  *
  * {
- *   "code": String
+ *   "code": RequestErrorCode
  *   "message": String
  *   "data": optional object
  * }
  */
 final Matcher isError = new LazyMatcher(() => new MatchesJsonObject(
   "Error", {
-    "code": isString,
+    "code": isRequestErrorCode,
     "message": isString
   }, optionalFields: {
     "data": isObject
@@ -1612,6 +1612,29 @@ final Matcher isRemoveContentOverlay = new LazyMatcher(() => new MatchesJsonObje
   }));
 
 /**
+ * RequestErrorCode
+ *
+ * enum {
+ *   GET_ERRORS_ERROR
+ *   INVALID_PARAMETER
+ *   INVALID_REQUEST
+ *   SERVER_ALREADY_STARTED
+ *   UNANALYZED_PRIORITY_FILES
+ *   UNKNOWN_REQUEST
+ *   UNSUPPORTED_FEATURE
+ * }
+ */
+final Matcher isRequestErrorCode = new MatchesEnum("RequestErrorCode", [
+  "GET_ERRORS_ERROR",
+  "INVALID_PARAMETER",
+  "INVALID_REQUEST",
+  "SERVER_ALREADY_STARTED",
+  "UNANALYZED_PRIORITY_FILES",
+  "UNKNOWN_REQUEST",
+  "UNSUPPORTED_FEATURE"
+]);
+
+/**
  * SearchId
  *
  * String