Add 'part of' in dart2js code.

lib/compiler/implementation/scanner/token.dart

 // Copyright (c) 2011, 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.
 
+part of scanner;
+
 const int EOF_TOKEN = 0;
 
 const int KEYWORD_TOKEN = $k;
 const int IDENTIFIER_TOKEN = $a;
 const int BAD_INPUT_TOKEN = $X;
 const int DOUBLE_TOKEN = $d;
 const int INT_TOKEN = $i;
 const int HEXADECIMAL_TOKEN = $x;
 const int STRING_TOKEN = $SQ;
 
@@ skipping 478 matching lines @@
 
 const PrecedenceInfo HEXADECIMAL_INFO =
   const PrecedenceInfo(const SourceString('hexadecimal'), 0, HEXADECIMAL_TOKEN);
 
 const PrecedenceInfo COMMENT_INFO =
   const PrecedenceInfo(const SourceString('comment'), 0, COMMENT_TOKEN);
 
 // For reporting lexical errors.
 const PrecedenceInfo ERROR_INFO =
   const PrecedenceInfo(const SourceString('?'), 0, UNKNOWN_TOKEN);