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

net/dns/dns_config_service.h

Index: net/dns/dns_config_service.h
diff --git a/net/dns/dns_config_service.h b/net/dns/dns_config_service.h
index bc3542d6092cbb123a4325dde1e7b4a00df7598f..4b77b68c51db353c8f23365aeb99bb994bb9f1b0 100644
--- a/net/dns/dns_config_service.h
+++ b/net/dns/dns_config_service.h
@@ -135,6 +135,8 @@ class NET_EXPORT_PRIVATE DnsConfigService
   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_;