Fix HttpBodyHandler to handle missing mimeType.

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;
 
 class _HttpHeaders implements HttpHeaders {
   _HttpHeaders(String this.protocolVersion)
       : _headers = new Map<String, List<String>>();
 
@@ skipping 614 matching lines @@
     int index = _value.indexOf("/");
     if (index == -1 || index == (_value.length - 1)) {
       _primaryType = _value.trim().toLowerCase();
       _subType = "";
     } else {
       _primaryType = _value.substring(0, index).trim().toLowerCase();
       _subType = _value.substring(index + 1).trim().toLowerCase();
     }
   }
 
+  String get mimeType => '$primaryType/$subType';
+
   String get primaryType => _primaryType;
 
   String get subType => _subType;
 
   String get charset => parameters["charset"];
 }
 
 
 class _Cookie implements Cookie {
   _Cookie([String this.name, String this.value]);
@@ skipping 117 matching lines @@
 
   String name;
   String value;
   DateTime expires;
   int maxAge;
   String domain;
   String path;
   bool httpOnly = false;
   bool secure = false;
 }