DNS: Add stubs for persisting data across restarts

net/dns/host_resolver_impl.h

Index: net/dns/host_resolver_impl.h
diff --git a/net/dns/host_resolver_impl.h b/net/dns/host_resolver_impl.h
index 68afccc6bf59f00f5964022ae41d93f8b4099ff8..54de1c8e4fa947fb67bdd4b6f695145a9d7b85de 100644
--- a/net/dns/host_resolver_impl.h
+++ b/net/dns/host_resolver_impl.h
@@ -16,6 +16,7 @@
 #include "base/strings/string_piece.h"
 #include "base/threading/non_thread_safe.h"
 #include "base/time/time.h"
+#include "base/timer/timer.h"
 #include "net/base/net_export.h"
 #include "net/base/network_change_notifier.h"
 #include "net/dns/host_cache.h"
@@ -153,6 +154,10 @@ class NET_EXPORT HostResolverImpl
                             HostCache::EntryStaleness* stale_info,
                             const BoundNetLog& source_net_log);
 
+  void InitializePersistence(
+      const PersistCallback& persist_callback,
+      std::unique_ptr<const base::Value> old_data) override;
+
   void set_proc_params_for_test(const ProcTaskParams& proc_params) {
     proc_params_ = proc_params;
   }
@@ -294,6 +299,12 @@ class NET_EXPORT HostResolverImpl
   // and resulted in |net_error|.
   void OnDnsTaskResolve(int net_error);
 
+  void SchedulePersist();
+  void DoPersist();
+
+  void ApplyPersistentData(std::unique_ptr<const base::Value>);
+  std::unique_ptr<const base::Value> GetPersistentData();
+
   // Allows the tests to catch slots leaking out of the dispatcher.  One
   // HostResolverImpl::Job could occupy multiple PrioritizedDispatcher job
   // slots.
@@ -350,6 +361,10 @@ class NET_EXPORT HostResolverImpl
   // tasks, but can be overridden for tests.
   scoped_refptr<base::TaskRunner> worker_task_runner_;
 
+  bool persist_initialized_;
+  PersistCallback persist_callback_;
+  base::OneShotTimer persist_timer_;
+
   base::WeakPtrFactory<HostResolverImpl> weak_ptr_factory_;
 
   base::WeakPtrFactory<HostResolverImpl> probe_weak_ptr_factory_;