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

net/http/http_response_info.h

Index: net/http/http_response_info.h
===================================================================
--- net/http/http_response_info.h	(revision 26596)
+++ net/http/http_response_info.h	(working copy)
@@ -7,14 +7,13 @@
 
 #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();