Remove "Default Address Family" behavior from the HostResolver.

This behavior was used to either force IPv4 resolution on dual-stack devices (using the --disable-ipv6 command-line flag) or to force IPv6 resolution.

Now that the flags have gone away, this behavior is no longer needed in the HostResolver.

BUG=344685

Review URL: https://codereview.chromium.org/1163903002

Cr-Commit-Position: refs/heads/master@{#333062}

net/dns/host_resolver.cc

@@ -100,10 +100,6 @@ HostResolver::RequestInfo::RequestInfo(const HostPortPair& host_port_pair)
 HostResolver::~HostResolver() {
 }
 
-AddressFamily HostResolver::GetDefaultAddressFamily() const {
-  return ADDRESS_FAMILY_UNSPECIFIED;
-}
-
 void HostResolver::SetDnsClientEnabled(bool enabled) {
 }
 

net/dns/host_resolver.h

@@ -167,13 +167,6 @@ class NET_EXPORT HostResolver {
   // has already run or the request was canceled.
   virtual void CancelRequest(RequestHandle req) = 0;
 
-  // Sets the default AddressFamily to use when requests have left it
-  // unspecified. For example, this could be used to restrict resolution
-  // results to AF_INET by passing in ADDRESS_FAMILY_IPV4, or to
-  // AF_INET6 by passing in ADDRESS_FAMILY_IPV6.
-  virtual void SetDefaultAddressFamily(AddressFamily address_family) {}
-  virtual AddressFamily GetDefaultAddressFamily() const;
-
   // Enable or disable the built-in asynchronous DnsClient.
   virtual void SetDnsClientEnabled(bool enabled);
 

net/dns/host_resolver_impl.cc

@@ -1844,10 +1844,8 @@ HostResolverImpl::HostResolverImpl(const Options& options, NetLog* net_log)
     : max_queued_jobs_(0),
       proc_params_(NULL, options.max_retry_attempts),
       net_log_(net_log),
-      default_address_family_(ADDRESS_FAMILY_UNSPECIFIED),
       received_dns_config_(false),
       num_dns_failures_(0),
-      probe_ipv6_support_(true),
       use_local_ipv6_(false),
       last_ipv6_probe_result_(true),
       resolved_known_ipv6_hostname_(false),
@@ -2032,16 +2030,6 @@ void HostResolverImpl::CancelRequest(RequestHandle req_handle) {
   job->CancelRequest(req);
 }
 
-void HostResolverImpl::SetDefaultAddressFamily(AddressFamily address_family) {
-  DCHECK(CalledOnValidThread());
-  default_address_family_ = address_family;
-  probe_ipv6_support_ = false;
-}
-
-AddressFamily HostResolverImpl::GetDefaultAddressFamily() const {
-  return default_address_family_;
-}
-
 void HostResolverImpl::SetDnsClientEnabled(bool enabled) {
   DCHECK(CalledOnValidThread());
 #if defined(ENABLE_BUILT_IN_DNS)
@@ -2088,14 +2076,8 @@ bool HostResolverImpl::ResolveAsIP(const Key& key,
 
   *net_error = OK;
   AddressFamily family = GetAddressFamily(*ip_number);
-  if (family == ADDRESS_FAMILY_IPV6 &&
-      !probe_ipv6_support_ &&
-      default_address_family_ == ADDRESS_FAMILY_IPV4) {
-    // Don't return IPv6 addresses if default address family is set to IPv4,
-    // and probes are disabled.
-    *net_error = ERR_NAME_NOT_RESOLVED;
-  } else if (key.address_family != ADDRESS_FAMILY_UNSPECIFIED &&
-             key.address_family != family) {
+  if (key.address_family != ADDRESS_FAMILY_UNSPECIFIED &&
+      key.address_family != family) {
     // Don't return IPv6 addresses for IPv4 queries, and vice versa.
     *net_error = ERR_NAME_NOT_RESOLVED;
   } else {
@@ -2208,22 +2190,18 @@ HostResolverImpl::Key HostResolverImpl::GetEffectiveKeyForRequest(
   AddressFamily effective_address_family = info.address_family();
 
   if (info.address_family() == ADDRESS_FAMILY_UNSPECIFIED) {
-    if (probe_ipv6_support_ && !use_local_ipv6_ &&
+    if (!use_local_ipv6_ &&
         // When resolving IPv4 literals, there's no need to probe for IPv6.
         // When resolving IPv6 literals, there's no benefit to artificially
         // limiting our resolution based on a probe.  Prior logic ensures
         // that this query is UNSPECIFIED (see info.address_family()
-        // check above) and that |default_address_family_| is UNSPECIFIED
-        // (|prove_ipv6_support_| is false if |default_address_family_| is
-        // set) so the code requesting the resolution should be amenable to
-        // receiving a IPv6 resolution.
+        // check above) so the code requesting the resolution should be amenable
+        // to receiving a IPv6 resolution.
         ip_number == nullptr) {
       if (!IsIPv6Reachable(net_log)) {
         effective_address_family = ADDRESS_FAMILY_IPV4;
         effective_flags |= HOST_RESOLVER_DEFAULT_FAMILY_SET_DUE_TO_NO_IPV6;
       }
-    } else {
-      effective_address_family = default_address_family_;
     }
   }
 

net/dns/host_resolver_impl.h

@@ -135,8 +135,6 @@ class NET_EXPORT HostResolverImpl
                        AddressList* addresses,
                        const BoundNetLog& source_net_log) override;
   void CancelRequest(RequestHandle req) override;
-  void SetDefaultAddressFamily(AddressFamily address_family) override;
-  AddressFamily GetDefaultAddressFamily() const override;
   void SetDnsClientEnabled(bool enabled) override;
   HostCache* GetHostCache() override;
   base::Value* GetDnsConfigAsValue() const override;
@@ -205,7 +203,7 @@ class NET_EXPORT HostResolverImpl
   // 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 IsIPv6Reachable(const BoundNetLog& net_log);
+  virtual bool IsIPv6Reachable(const BoundNetLog& net_log);
 
   // Records the result in cache if cache is present.
   void CacheResult(const Key& key,
@@ -268,9 +266,6 @@ class NET_EXPORT HostResolverImpl
 
   NetLog* net_log_;
 
-  // Address family to use when the request doesn't specify one.
-  AddressFamily default_address_family_;
-
   // If present, used by DnsTask and ServeFromHosts to resolve requests.
   scoped_ptr<DnsClient> dns_client_;
 
@@ -281,10 +276,6 @@ class NET_EXPORT HostResolverImpl
   // Number of consecutive failures of DnsTask, counted when fallback succeeds.
   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_;