Delete "Net.UnspecResolvedIPv6" histogram

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 <stddef.h>
 #include <stdint.h>
 
@@ skipping 346 matching lines @@
   // https://crbug.com/696569 for further context.
   bool assume_ipv6_failure_on_wifi_;
 
   // 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_;
 
   // Task runner used for DNS lookups using the platform resolver, and other
   // blocking operations. Usually just the WorkerPool's task runner for slow
   // tasks, but can be overridden for tests.
   scoped_refptr<base::TaskRunner> worker_task_runner_;
@@ skipping 20 matching lines @@
 // This function is only exposed so it can be unit-tested.
 // TODO(tfarina): It would be better to change the tests so this function
 // gets exercised indirectly through HostResolverImpl.
 NET_EXPORT_PRIVATE bool ResolveLocalHostname(base::StringPiece host,
                                              uint16_t port,
                                              AddressList* address_list);
 
 }  // namespace net
 
 #endif  // NET_DNS_HOST_RESOLVER_IMPL_H_