Add enumeration of the HTTP headers

runtime/bin/http_impl.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.
 
 class _HttpHeaders implements HttpHeaders {
   _HttpHeaders() : _headers = new Map<String, List<String>>();
 
   List<String> operator[](String name) {
     name = name.toLowerCase();
     return _headers[name];
@@ skipping 37 matching lines @@
       }
     }
   }
 
   void removeAll(String name) {
     _checkMutable();
     name = name.toLowerCase();
     _headers.remove(name);
   }
 
+  void forEach(void f(String name, List<String> values)) {
+    _headers.forEach(f);
+  }
+
   String get host() => _host;
 
   void set host(String host) {
     _checkMutable();
     _host = host;
     _updateHostHeader();
   }
 
   int get port() => _port;
 
@@ skipping 1471 matching lines @@
 }
 
 
 class _DetachedSocket implements DetachedSocket {
   _DetachedSocket(this._socket, this._unparsedData);
   Socket get socket() => _socket;
   List<int> get unparsedData() => _unparsedData;
   Socket _socket;
   List<int> _unparsedData;
 }