Add error codes to server protocol (#25958).

pkg/analysis_server/lib/src/protocol_server.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library protocol.server;
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/plugin/protocol/protocol_dart.dart';
 import 'package:analysis_server/src/services/correction/fix.dart';
 import 'package:analysis_server/src/services/search/search_engine.dart'
@@ skipping 93 matching lines @@
     if (lineInfo != null) {
       engine.LineInfo_Location lineLocation = lineInfo.getLocation(offset);
       if (lineLocation != null) {
         startLine = lineLocation.lineNumber;
         startColumn = lineLocation.columnNumber;
       }
     }
     location = new Location(file, offset, length, startLine, startColumn);
   }
 
-  // Deafult to the error's severity if none is specified.
+  // Default to the error's severity if none is specified.
   errorSeverity ??= errorCode.errorSeverity;
 
   // done
   var severity = new AnalysisErrorSeverity(errorSeverity.name);
   var type = new AnalysisErrorType(errorCode.type.name);
   String message = error.message;
+  String code = errorCode.name.toLowerCase();
   String correction = error.correction;
   bool fix = hasFix(error.errorCode);
-  return new AnalysisError(severity, type, location, message,
+  return new AnalysisError(severity, type, location, message, code,
       correction: correction, hasFix: fix);
 }
 
 /**
  * Create a Location based on an [engine.Element].
  */
 Location newLocation_fromElement(engine.Element element) {
   engine.AnalysisContext context = element.context;
   engine.Source source = element.source;
   if (context == null || source == null) {
@@ skipping 122 matching lines @@
     if (lineInfo != null) {
       engine.LineInfo_Location offsetLocation =
           lineInfo.getLocation(range.offset);
       startLine = offsetLocation.lineNumber;
       startColumn = offsetLocation.columnNumber;
     }
   }
   return new Location(
       source.fullName, range.offset, range.length, startLine, startColumn);
 }