[net/dns] Suppress multiple DnsConfig withdrawals after timeout.

net/dns/dns_config_service.h

 // Copyright (c) 2012 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_DNS_DNS_CONFIG_SERVICE_H_
 #define NET_DNS_DNS_CONFIG_SERVICE_H_
 #pragma once
 
 #include <map>
 #include <string>
@@ skipping 117 matching lines @@
 
   CallbackType callback_;
 
   DnsConfig dns_config_;
 
   // True after On*Read, before Invalidate*. Tells if the config is complete.
   bool have_config_;
   bool have_hosts_;
   // True if receiver needs to be updated when the config becomes complete.
   bool need_update_;
+  // True if the last config sent was empty (instead of |dns_config_|).
+  bool last_sent_empty_;
 
   // Started in Invalidate*, cleared in On*Read.
   base::OneShotTimer<DnsConfigService> timer_;
 
   DISALLOW_COPY_AND_ASSIGN(DnsConfigService);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_DNS_CONFIG_SERVICE_H_