Support `void` as generic argument.

pkg/front_end/lib/src/scanner/token.dart

 // Copyright (c) 2016, 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.
 
 /**
  * Defines the tokens that are produced by the scanner, used by the parser, and
  * referenced from the [AST structure](ast.dart).
  */
 import 'dart:collection';
 
@@ skipping 267 matching lines @@
   static const Keyword THROW = const Keyword("throw");
 
   static const Keyword TRUE = const Keyword("true");
 
   static const Keyword TRY = const Keyword("try");
 
   static const Keyword TYPEDEF = const Keyword("typedef", isBuiltIn: true);
 
   static const Keyword VAR = const Keyword("var");
 
-  static const Keyword VOID = const Keyword("void");
+  static const Keyword VOID = const Keyword("void", isBuiltIn: true);
 
   static const Keyword WHILE = const Keyword("while");
 
   static const Keyword WITH = const Keyword("with");
 
   static const Keyword YIELD = const Keyword("yield", isPseudo: true);
 
   static const List<Keyword> values = const <Keyword>[
     ABSTRACT,
     AS,
@@ skipping 1256 matching lines @@
 
   void set precedingComments(CommentToken comment) {
     _precedingComment = comment;
     _setCommentParent(_precedingComment);
   }
 
   @override
   Token copy() =>
       new TokenWithComment(type, offset, copyComments(precedingComments));
 }