Add Cronet experimental option to disable ipv6

components/cronet/stale_host_resolver.h

 // Copyright 2016 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 COMPONENTS_CRONET_STALE_HOST_RESOLVER_H_
 #define COMPONENTS_CRONET_STALE_HOST_RESOLVER_H_
 
 #include <unordered_set>
 
 #include "net/dns/host_resolver.h"
@@ skipping 55 matching lines @@
               const net::NetLogWithSource& net_log) override;
 
   // The remaining public methods pass through to the inner resolver:
 
   int ResolveFromCache(const RequestInfo& info,
                        net::AddressList* addresses,
                        const net::NetLogWithSource& net_log) override;
   void SetDnsClientEnabled(bool enabled) override;
   net::HostCache* GetHostCache() override;
   std::unique_ptr<base::Value> GetDnsConfigAsValue() const override;
+  void SetDefaultAddressFamily(net::AddressFamily address_family) override;
+  net::AddressFamily GetDefaultAddressFamily() const override;
 
  private:
   class RequestImpl;
 
   // Called from |Request| when a request is complete and can be destroyed.
   void OnRequestComplete(Request* request);
 
   // The underlying HostResolverImpl that will be used to make cache and network
   // requests.
   std::unique_ptr<net::HostResolverImpl> inner_resolver_;
 
   // Options that govern when a stale response can or can't be returned.
   StaleOptions options_;
 
   DISALLOW_COPY_AND_ASSIGN(StaleHostResolver);
 };
 
 }  // namespace cronet
 
 #endif  // COMPONENTS_CRONET_STALE_HOST_RESOLVER_H_