Revert "Remaining private libs"

sdk/lib/io/http_headers.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";
+part of "io.dart";
 
 class _HttpHeaders implements HttpHeaders {
   final Map<String, List<String>> _headers;
   final String protocolVersion;
 
   bool _mutable = true; // Are the headers currently mutable?
   List<String> _noFoldingHeaders;
 
   int _contentLength = -1;
   bool _persistentConnection = true;
@@ skipping 975 matching lines @@
           (codeUnit >= 0x23 && codeUnit <= 0x2B) ||
           (codeUnit >= 0x2D && codeUnit <= 0x3A) ||
           (codeUnit >= 0x3C && codeUnit <= 0x5B) ||
           (codeUnit >= 0x5D && codeUnit <= 0x7E))) {
         throw new FormatException(
             "Invalid character in cookie value, code unit: '$codeUnit'");
       }
     }
   }
 }