Handle TypeVariable and TypeVariables in AstBuilder.

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 BeginGroupToken, Token;
 
 import '../util/link.dart' show Link;
 
@@ skipping 610 matching lines @@
   void endTypeArguments(int count, Token beginToken, Token endToken) {
     logEvent("TypeArguments");
   }
 
   void handleNoTypeArguments(Token token) {
     logEvent("NoTypeArguments");
   }
 
   void beginTypeVariable(Token token) {}
 
+  /// Handle the end of a type formal parameter (e.g. "X extends Y").
+  /// Substructures:
+  /// - Name (identifier)
+  /// - Type bound
   void endTypeVariable(Token token, Token extendsOrSuper) {
     logEvent("TypeVariable");
   }
 
   void beginTypeVariables(Token token) {}
 
   void endTypeVariables(int count, Token beginToken, Token endToken) {
     logEvent("TypeVariables");
   }
 
@@ skipping 247 matching lines @@
 
   final Map arguments;
 
   ParserError(this.beginOffset, this.endOffset, this.kind, this.arguments);
 
   ParserError.fromTokens(Token begin, Token end, ErrorKind kind, Map arguments)
       : this(begin.charOffset, end.charOffset + end.charCount, kind, arguments);
 
   String toString() => "@${beginOffset}: $kind $arguments";
 }