Move parser helper classes to own files and clean them up.

pkg/front_end/lib/src/fasta/parser/listener.dart

 // Copyright (c) 2012, 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.parser.listener;
 
+import '../../scanner/token.dart' show BeginToken, Token, TokenType;
+
 import '../fasta_codes.dart' show Message;
 
-import '../../scanner/token.dart' show BeginToken, Token, TokenType;
-
 import '../util/link.dart' show Link;
 
-import 'parser.dart' show Assert, FormalParameterType, MemberKind;
+import 'assert.dart' show Assert;
+
+import 'formal_parameter_kind.dart' show FormalParameterKind;
 
 import 'identifier_context.dart' show IdentifierContext;
 
+import 'member_kind.dart' show MemberKind;
+
+import 'parser_error.dart' show ParserError;
+
 /// A parser event listener that does nothing except throw exceptions
 /// on parser errors.
 ///
 /// Events are methods that begin with one of: `begin`, `end`, or `handle`.
 ///
 /// Events starting with `begin` and `end` come in pairs. Normally, a
 /// `beginFoo` event is followed by an `endFoo` event. There's a few exceptions
 /// documented below.
 ///
 /// Events starting with `handle` are used when isn't possible to have a begin
@@ skipping 162 matching lines @@
   void beginFactoryMethod(Token token) {}
 
   void endFactoryMethod(
       Token beginToken, Token factoryKeyword, Token endToken) {
     logEvent("FactoryMethod");
   }
 
   void beginFormalParameter(Token token, MemberKind kind) {}
 
   void endFormalParameter(Token thisKeyword, Token nameToken,
-      FormalParameterType kind, MemberKind memberKind) {
+      FormalParameterKind kind, MemberKind memberKind) {
     logEvent("FormalParameter");
   }
 
   void handleNoFormalParameters(Token token, MemberKind kind) {
     logEvent("NoFormalParameters");
   }
 
   void beginFormalParameters(Token token, MemberKind kind) {}
 
   void endFormalParameters(
@@ skipping 885 matching lines @@
   void discardTypeReplacedWithCommentTypeAssign() {}
 
   /// Creates a new synthetic token whose `next` pointer points to [next].
   ///
   /// If [next] is `null`, `null` is returned.
   Token newSyntheticToken(Token next) {
     if (next == null) return null;
     return new Token(TokenType.RECOVERY, next.charOffset)..next = next;
   }
 }
-
-class ParserError {
-  /// Character offset from the beginning of file where this error starts.
-  final int beginOffset;
-
-  /// Character offset from the beginning of file where this error ends.
-  final int endOffset;
-
-  final Message message;
-
-  ParserError(this.beginOffset, this.endOffset, this.message);
-
-  ParserError.fromTokens(Token begin, Token end, Message message)
-      : this(begin.charOffset, end.charOffset + end.charCount, message);
-
-  String toString() => "@${beginOffset}: ${message.message}\n${message.tip}";
-}