Reduce frequency of IPv6 probes in HostResolverImpl.

net/dns/host_resolver_impl.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_HOST_RESOLVER_IMPL_H_
 #define NET_DNS_HOST_RESOLVER_IMPL_H_
 
 #include <map>
 
 #include "base/basictypes.h"
@@ skipping 182 matching lines @@
                       AddressList* addresses);
 
   // Callback from HaveOnlyLoopbackAddresses probe.
   void SetHaveOnlyLoopbackAddresses(bool result);
 
   // Returns the (hostname, address_family) key to use for |info|, choosing an
   // "effective" address family by inheriting the resolver's default address
   // family when the request leaves it unspecified.
   Key GetEffectiveKeyForRequest(const RequestInfo& info,
                                 const IPAddressNumber* ip_number,
-                                const BoundNetLog& net_log) const;
+                                const BoundNetLog& net_log);
+
+  // Probes IPv6 support and returns true if IPv6 support is enabled.
+  // Results are cached, i.e. when called repeatedly this method returns result
+  // from the first probe for some time before probing again.
+  bool ProbeIpv6SupportCached(const BoundNetLog& net_log);
 
   // Records the result in cache if cache is present.
   void CacheResult(const Key& key,
                    const HostCache::Entry& entry,
                    base::TimeDelta ttl);
 
   // Removes |job| from |jobs_|, only if it exists.
   void RemoveJob(Job* job);
 
   // Aborts all in progress jobs with ERR_NETWORK_CHANGED and notifies their
@@ skipping 63 matching lines @@
   unsigned num_dns_failures_;
 
   // True if probing is done for each Request to set address family. When false,
   // explicit setting in |default_address_family_| is used.
   bool probe_ipv6_support_;
 
   // True if DnsConfigService detected that system configuration depends on
   // local IPv6 connectivity. Disables probing.
   bool use_local_ipv6_;
 
+  base::TimeTicks last_ipv6_probe_time_;
+  bool last_ipv6_probe_result_;
+
   // True iff ProcTask has successfully resolved a hostname known to have IPv6
   // addresses using ADDRESS_FAMILY_UNSPECIFIED. Reset on IP address change.
   bool resolved_known_ipv6_hostname_;
 
   // Any resolver flags that should be added to a request by default.
   HostResolverFlags additional_resolver_flags_;
 
   // Allow fallback to ProcTask if DnsTask fails.
   bool fallback_to_proctask_;
 
   base::WeakPtrFactory<HostResolverImpl> weak_ptr_factory_;
 
   base::WeakPtrFactory<HostResolverImpl> probe_weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(HostResolverImpl);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_HOST_RESOLVER_IMPL_H_