Remove deprecated Strings class.

utils/peg/pegparser.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.
 
 library Peg Parser;
 
 /*
  * The following functions are combinators for building Rules.
  *
  * A rule is one of the following
@@ skipping 257 matching lines @@
     var message = 'unexpected error';
     if (!state.max_rule.isEmpty) {
       var s = new Set();
       for (var rule in state.max_rule)
         s.add(rule.description());
       var tokens = new List<String>.from(s);
       tokens.sort((a, b) =>
                   a.startsWith("'") == b.startsWith("'")
                       ? a.compareTo(b)
                       : a.startsWith("'") ? +1 : -1);
-      var expected = Strings.join(tokens, ' or ');
+      var expected = tokens.join(' or ');
       var found = state.max_pos == state._end ? 'end of file'
           : "'${state._text[state.max_pos]}'";
       message = 'Expected $expected but found $found';
     }
     int start = state.max_pos;
     int end = start;
     while (start >= 1 && state._text[start - 1] != '\n') --start;
     while (end < state._text.length && state._text[end] != '\n') ++end;
     var line = state._text.substring(start, end);
     var indicator = '';
@@ skipping 560 matching lines @@
   add(s);
   add(t);
   add(u);
   add(v);
   add(w);
   add(x);
   add(y);
   add(z);
   return list;
 }