Add back "default address family" to HostResolver

net/dns/host_resolver.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_H_
 #define NET_DNS_HOST_RESOLVER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 195 matching lines @@
   typedef base::Callback<void(std::unique_ptr<const base::Value>)>
       PersistCallback;
   // Configures the HostResolver to be able to persist data (e.g. observed
   // performance) between sessions. |persist_callback| is a callback that will
   // be called when the HostResolver wants to persist data; |old_data| is the
   // data last persisted by the resolver on the previous session.
   virtual void InitializePersistence(
       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. This is used only to disable
+  // IPv6 in Cronet, and can be removed when support for the option is no longer
+  // needed. See http://crbug.com/696569.
+  virtual void SetDefaultAddressFamily(AddressFamily address_family) {}

[xunjieli, 2017/02/27 15:41:38]

Please add a NOTREACHED() here.
Mentioning Cronet in net/ is a layering volation. Please rework the comment.

[mgersh, 2017/02/28 16:49:06]

Done.

+  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).
   static std::unique_ptr<HostResolver> CreateSystemResolver(
       const Options& options,
       NetLog* net_log);
   // Same, but explicitly returns the HostResolverImpl. Only used by
   // StaleHostResolver in cronet.
   static std::unique_ptr<HostResolverImpl> CreateSystemResolverImpl(
       const Options& options,
       NetLog* net_log);
 
   // As above, but uses default parameters.
   static std::unique_ptr<HostResolver> CreateDefaultResolver(NetLog* net_log);
   // Same, but explicitly returns the HostResolverImpl. Only used by
   // StaleHostResolver in cronet.
   static std::unique_ptr<HostResolverImpl> CreateDefaultResolverImpl(
       NetLog* net_log);
 
  protected:
   HostResolver();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(HostResolver);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_HOST_RESOLVER_H_