DNS: Add stubs for persisting data across restarts

net/dns/dns_session.cc

Index: net/dns/dns_session.cc
diff --git a/net/dns/dns_session.cc b/net/dns/dns_session.cc
index 82b947e12f72b703a3c5eeecbf4da41c62d74fc3..f3ddc68506e66e7501a0e4d253bb6d1b9fb0333f 100644
--- a/net/dns/dns_session.cc
+++ b/net/dns/dns_session.cc
@@ -19,6 +19,7 @@
 #include "base/rand_util.h"
 #include "base/stl_util.h"
 #include "base/time/time.h"
+#include "base/values.h"
 #include "net/base/ip_endpoint.h"
 #include "net/base/net_errors.h"
 #include "net/dns/dns_config_service.h"
@@ -289,6 +290,12 @@ std::unique_ptr<StreamSocket> DnsSession::CreateTCPSocket(
   return socket_pool_->CreateTCPSocket(server_index, source);
 }
 
+void DnsSession::ApplyPersistentData(const base::Value& data) {}
+
+std::unique_ptr<const base::Value> DnsSession::GetPersistentData() const {
+  return std::unique_ptr<const base::Value>();
+}
+
 // Release a socket.
 void DnsSession::FreeSocket(unsigned server_index,
                             std::unique_ptr<DatagramClientSocket> socket) {