DNS: Add stubs for persisting data across restarts

net/dns/dns_test_util.cc

Index: net/dns/dns_test_util.cc
diff --git a/net/dns/dns_test_util.cc b/net/dns/dns_test_util.cc
index 6f94b7f9e29873e003b81abd6437cf5399ba9518..5ee0f1d15217fec747fcf0473b04ecd232cc121f 100644
--- a/net/dns/dns_test_util.cc
+++ b/net/dns/dns_test_util.cc
@@ -221,6 +221,12 @@ AddressSorter* MockDnsClient::GetAddressSorter() {
   return address_sorter_.get();
 }
 
+void MockDnsClient::ApplyPersistentData(const base::Value& data) {}
+
+std::unique_ptr<const base::Value> MockDnsClient::GetPersistentData() const {
+  return std::unique_ptr<const base::Value>();
+}
+
 void MockDnsClient::CompleteDelayedTransactions() {
   factory_->CompleteDelayedTransactions();
 }