Because we use scoped_refptr<> to the HttpResponseInfo...

net/http/http_response_info.h

 // Copyright (c) 2006-2009 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_HTTP_HTTP_RESPONSE_INFO_H_
 #define NET_HTTP_HTTP_RESPONSE_INFO_H_
 
 #include "base/time.h"
 #include "net/base/auth.h"
+#include "net/base/ssl_cert_request_info.h"
 #include "net/base/ssl_info.h"
+#include "net/http/http_response_headers.h"
 #include "net/http/http_vary_data.h"
 
 namespace net {
 
-class HttpResponseHeaders;
-class SSLCertRequestInfo;
-
 class HttpResponseInfo {
  public:
   HttpResponseInfo();
   ~HttpResponseInfo();
   // Default copy-constructor and assignment operator are OK!
 
   // The following is only defined if the request_time member is set.
   // If this response was resurrected from cache, then this bool is set, and
   // request_time may corresponds to a time "far" in the past.  Note that
   // stale content (perhaps un-cacheable) may be fetched from cache subject to
@@ skipping 26 matching lines @@
   // The parsed response headers and status line.
   scoped_refptr<HttpResponseHeaders> headers;
 
   // The "Vary" header data for this response.
   HttpVaryData vary_data;
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_RESPONSE_INFO_H_