Add back "default address family" to HostResolver

net/dns/host_resolver.h

Index: net/dns/host_resolver.h
diff --git a/net/dns/host_resolver.h b/net/dns/host_resolver.h
index fe38138f5c6934da06aa4788edfc1b3739460263..33cdd34e7200a59b7a5b25dbefbde49a6ca36ce9 100644
--- a/net/dns/host_resolver.h
+++ b/net/dns/host_resolver.h
@@ -213,6 +213,14 @@ class NET_EXPORT HostResolver {
       const PersistCallback& persist_callback,
       std::unique_ptr<const base::Value> old_data);
 
+  // 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. See http://crbug.com/696569 for
+  // why this option is necessary.
+  virtual void SetDefaultAddressFamily(AddressFamily address_family);
+  virtual AddressFamily GetDefaultAddressFamily() const;
+
   // Creates a HostResolver implementation that queries the underlying system.
   // (Except if a unit-test has changed the global HostResolverProc using
   // ScopedHostResolverProc to intercept requests to the system).