Rename Error to RequestError in analysis server API.

pkg/analysis_server/lib/src/socket_server.dart

Index: pkg/analysis_server/lib/src/socket_server.dart
diff --git a/pkg/analysis_server/lib/src/socket_server.dart b/pkg/analysis_server/lib/src/socket_server.dart
index 9623ae40201c5a125f3727ca0e34b2dd58922b18..cffffa0813e5275f957e029b225e0614ec590215 100644
--- a/pkg/analysis_server/lib/src/socket_server.dart
+++ b/pkg/analysis_server/lib/src/socket_server.dart
@@ -52,7 +52,8 @@ class SocketServer {
    */
   void createAnalysisServer(ServerCommunicationChannel serverChannel) {
     if (analysisServer != null) {
-      RequestError error = new RequestError.serverAlreadyStarted();
+      RequestError error = new RequestError(
+          RequestErrorCode.SERVER_ALREADY_STARTED, "Server already started");
       serverChannel.sendResponse(new Response('', error: error));
       serverChannel.listen((Request request) {
         serverChannel.sendResponse(new Response(request.id, error: error));