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

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

Index: pkg/front_end/lib/src/fasta/parser/listener.dart
diff --git a/pkg/front_end/lib/src/fasta/parser/listener.dart b/pkg/front_end/lib/src/fasta/parser/listener.dart
index 7cf522b937660c2e7b175dfc1356e5e810a1a0f7..8639f9d4278bc0795da426fc625c580319c7313d 100644
--- a/pkg/front_end/lib/src/fasta/parser/listener.dart
+++ b/pkg/front_end/lib/src/fasta/parser/listener.dart
@@ -4,16 +4,22 @@
 
 library fasta.parser.listener;
 
-import '../fasta_codes.dart' show Message;
-
 import '../../scanner/token.dart' show BeginToken, Token, TokenType;
 
+import '../fasta_codes.dart' show Message;
+
 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.
 ///
@@ -196,7 +202,7 @@ class Listener {
   void beginFormalParameter(Token token, MemberKind kind) {}
 
   void endFormalParameter(Token thisKeyword, Token nameToken,
-      FormalParameterType kind, MemberKind memberKind) {
+      FormalParameterKind kind, MemberKind memberKind) {
     logEvent("FormalParameter");
   }
 
@@ -1102,20 +1108,3 @@ class Listener {
     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}";
-}