Reduce header dependencies in net/

net/base/net_module.h

 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_BASE_NET_MODULE_H__
 #define NET_BASE_NET_MODULE_H__
 
-#include <string>
-
 #include "base/basictypes.h"
 #include "base/string_piece.h"
 
 namespace net {
 
 // Defines global initializers and associated methods for the net module.
 //
 // The network module does not have direct access to the way application
 // resources are stored and fetched by the embedding application (e.g., it
 // cannot see the ResourceBundle class used by Chrome), so it uses this API to
@@ skipping 11 matching lines @@
   // resource provider.
   static StringPiece GetResource(int key);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(NetModule);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_NET_MODULE_H__