Implement generalized function types.

pkg/front_end/lib/src/fasta/fasta_codes.dart

 // Copyright (c) 2017, 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 fasta.codes;
 
 import 'package:front_end/src/scanner/token.dart' show Token;
 
 part 'fasta_codes_generated.dart';
 
 class FastaCode<T> {
+  final String name;
+
   final String template;
 
   final String tip;
 
   final String analyzerCode;
 
   final String dart2jsCode;
 
   final T format;
 
-  const FastaCode(
+  const FastaCode(this.name,
       {this.template,
       this.tip,
       this.analyzerCode,
       this.dart2jsCode,
       this.format});
+
+  String toString() => name;
 }
 
 class FastaMessage {
   final Uri uri;
 
   final int charOffset;
 
   final String message;
 
   final String tip;
 
   final FastaCode code;
 
   final Map<String, dynamic> arguments;
 
   const FastaMessage(this.uri, this.charOffset, this.code,
       {this.message, this.tip, this.arguments});
 }