Remove deprecated string features.

pkg/yaml/lib/model.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.
 
 part of yaml;
 
 // This file contains the node classes for the internal representations of YAML
 // documents. These nodes are used for both the serialization tree and the
 // representation graph.
 
@@ skipping 132 matching lines @@
       // 20 is the maximum value for this argument, which we use since YAML
       // doesn't specify a maximum.
       return value.toStringAsExponential(20).
         replaceFirst(new RegExp("0+e"), "e");
     }
 
     if (value is String) {
       // TODO(nweiz): This could be faster if we used a RegExp to check for
       // special characters and short-circuited if they didn't exist.
 
-      var escapedValue = value.charCodes.map((c) {
+      var escapedValue = value.codeUnits.map((c) {
         switch (c) {
         case _Parser.TAB: return "\\t";
         case _Parser.LF: return "\\n";
         case _Parser.CR: return "\\r";
         case _Parser.DOUBLE_QUOTE: return '\\"';
         case _Parser.NULL: return "\\0";
         case _Parser.BELL: return "\\a";
         case _Parser.BACKSPACE: return "\\b";
         case _Parser.VERTICAL_TAB: return "\\v";
         case _Parser.FORM_FEED: return "\\f";
@@ skipping 61 matching lines @@
     var strContent = content.keys
         .map((k) => '${k}: ${content[k]}')
         .join(', ');
     return '$tag {$strContent}';
   }
 
   int get hashCode => super.hashCode ^ _hashCode(content);
 
   visit(_Visitor v) => v.visitMapping(this);
 }