Modify scanner and parser to be standalone packages.

pkg/dart_scanner/lib/src/precedence.dart

 // Copyright (c) 2015, 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 dart2js.tokens.precedence.constants;
+library scanner.precedence;
 
-import 'precedence.dart' show PrecedenceInfo;
 import 'token_constants.dart';
 
+class PrecedenceInfo {
+  final String value;
+  final int precedence;
+  final int kind;
+
+  const PrecedenceInfo(this.value, this.precedence, this.kind);
+
+  toString() => 'PrecedenceInfo($value, $precedence, $kind)';
+}
+
 // TODO(ahe): The following are not tokens in Dart.
 const PrecedenceInfo BACKPING_INFO =
     const PrecedenceInfo('`', 0, BACKPING_TOKEN);
 const PrecedenceInfo BACKSLASH_INFO =
     const PrecedenceInfo('\\', 0, BACKSLASH_TOKEN);
 const PrecedenceInfo PERIOD_PERIOD_PERIOD_INFO =
     const PrecedenceInfo('...', 0, PERIOD_PERIOD_PERIOD_TOKEN);
 
 /**
  * The cascade operator has the lowest precedence of any operator
@@ skipping 160 matching lines @@
     const PrecedenceInfo('\${', 0, STRING_INTERPOLATION_TOKEN);
 
 const PrecedenceInfo STRING_INTERPOLATION_IDENTIFIER_INFO =
     const PrecedenceInfo('\$', 0, STRING_INTERPOLATION_IDENTIFIER_TOKEN);
 
 const PrecedenceInfo HEXADECIMAL_INFO =
     const PrecedenceInfo('hexadecimal', 0, HEXADECIMAL_TOKEN);
 
 const PrecedenceInfo COMMENT_INFO =
     const PrecedenceInfo('comment', 0, COMMENT_TOKEN);