DNS: Add stubs for persisting data across restarts

net/dns/host_resolver.h

 // Copyright (c) 2012 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 NET_DNS_HOST_RESOLVER_H_
 #define NET_DNS_HOST_RESOLVER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 168 matching lines @@
   virtual void SetDnsClientEnabled(bool enabled);
 
   // Returns the HostResolverCache |this| uses, or NULL if there isn't one.
   // Used primarily to clear the cache and for getting debug information.
   virtual HostCache* GetHostCache();
 
   // Returns the current DNS configuration |this| is using, as a Value, or
   // nullptr if it's configured to always use the system host resolver.
   virtual std::unique_ptr<base::Value> GetDnsConfigAsValue() const;
 
+  typedef base::Callback<void(std::unique_ptr<const base::Value>)>
+      PersistCallback;
+  // Configures the HostResolver to be able to persist data (e.g. observed
+  // performance) between sessions. |persist_callback| is a callback that will
+  // be called when the HostResolver wants to persist data; |old_data| is the
+  // data last persisted by the resolver on the previous session.
+  virtual void InitializePersistence(
+      const PersistCallback& persist_callback,
+      std::unique_ptr<const base::Value> old_data);
+
   // Creates a HostResolver implementation that queries the underlying system.
   // (Except if a unit-test has changed the global HostResolverProc using
   // ScopedHostResolverProc to intercept requests to the system).
   static std::unique_ptr<HostResolver> CreateSystemResolver(
       const Options& options,
       NetLog* net_log);
 
   // As above, but uses default parameters.
   static std::unique_ptr<HostResolver> CreateDefaultResolver(NetLog* net_log);
 
  protected:
   HostResolver();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(HostResolver);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_HOST_RESOLVER_H_