Add Cronet experimental option to disable ipv6

components/cronet/stale_host_resolver.cc

Index: components/cronet/stale_host_resolver.cc
diff --git a/components/cronet/stale_host_resolver.cc b/components/cronet/stale_host_resolver.cc
index 2d4c0779730c8b35e70c3ecd7d4f19a9e165bcfd..7687bd330de24b05d707b50d85719230825cf008 100644
--- a/components/cronet/stale_host_resolver.cc
+++ b/components/cronet/stale_host_resolver.cc
@@ -10,6 +10,7 @@
 #include "base/stl_util.h"
 #include "base/timer/timer.h"
 #include "base/values.h"
+#include "net/base/address_family.h"
 #include "net/base/net_errors.h"
 #include "net/dns/dns_util.h"
 #include "net/dns/host_resolver_impl.h"
@@ -397,4 +398,13 @@ std::unique_ptr<base::Value> StaleHostResolver::GetDnsConfigAsValue() const {
   return inner_resolver_->GetDnsConfigAsValue();
 }
 
+void StaleHostResolver::SetDefaultAddressFamily(

[xunjieli, 2017/02/27 15:37:39]

Suggest removing the overrides and relying on the default implementation for the
StaleDns resolver.

Mixing two experiments makes reasoning difficult. If we have one bug in one
experiment, we can't isolate it. In the case of StaleDns, we can potentially
persist ipv6-disabled dns results. In subsequent sessions, we might revert to
default behavior (who knows maybe ipv4 is broken for some reason.) and find out
we may or may not use the default behavior... Suggest adding a check to make
sure this and "ipv6 disable" are not enabled at the same time. 

[mgersh, 2017/02/28 18:29:57]

Done.

+    net::AddressFamily address_family) {
+  inner_resolver_->SetDefaultAddressFamily(address_family);
+}
+
+net::AddressFamily StaleHostResolver::GetDefaultAddressFamily() const {
+  return inner_resolver_->GetDefaultAddressFamily();
+}
+
 }  // namespace net