Remove deprecated string features.

sdk/lib/io/http_parser.dart

 // Copyright (c) 2013, 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 dart.io;
 
 // Global constants.
 class _Const {
   // Bytes for "HTTP".
   static const HTTP = const [72, 84, 84, 80];
@@ skipping 702 matching lines @@
       } else if (headerValue[index] == " " || headerValue[index] == "\t") {
         start++;
       }
       index++;
     }
     tokens.add(headerValue.substring(start, index));
     return tokens;
   }
 
   int _toLowerCase(int byte) {
-    final int aCode = "A".charCodeAt(0);
-    final int zCode = "Z".charCodeAt(0);
-    final int delta = "a".charCodeAt(0) - aCode;
+    final int aCode = "A".codeUnitAt(0);
+    final int zCode = "Z".codeUnitAt(0);
+    final int delta = "a".codeUnitAt(0) - aCode;
     return (aCode <= byte && byte <= zCode) ? byte + delta : byte;
   }
 
   int _expect(int val1, int val2) {
     if (val1 != val2) {
       throw new HttpParserException("Failed to parse HTTP");
     }
   }
 
   int _expectHexDigit(int byte) {
@@ skipping 42 matching lines @@
   Function error;
   Function closed;
 }
 
 
 class HttpParserException implements Exception {
   const HttpParserException([String this.message = ""]);
   String toString() => "HttpParserException: $message";
   final String message;
 }