DNS: Let requests specify a callback for future cache hits

net/dns/host_cache.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_CACHE_H_
 #define NET_DNS_HOST_CACHE_H_
 
 #include <stddef.h>
 
 #include <functional>
@@ skipping 95 matching lines @@
     base::TimeTicks expires_;
     // Copied from the cache's network_changes_ when the entry is set; can0
     // later be compared to it to see if the entry was received on the current
     // network.
     int network_changes_;
     int total_hits_;
     int stale_hits_;
   };
 
   using EntryMap = std::map<Key, Entry>;
+  using EvictionCallback = base::Callback<void(const Key&, const Entry&)>;
 
   // Constructs a HostCache that stores up to |max_entries|.
   explicit HostCache(size_t max_entries);
 
   ~HostCache();
 
   // Returns a pointer to the entry for |key|, which is valid at time
   // |now|. If there is no such entry, returns NULL.
   const Entry* Lookup(const Key& key, base::TimeTicks now);
 
   // Returns a pointer to the entry for |key|, whether it is valid or stale at
   // time |now|. Fills in |stale_out| with information about how stale it is.
   // If there is no entry for |key| at all, returns NULL.
   const Entry* LookupStale(const Key& key,
                            base::TimeTicks now,
                            EntryStaleness* stale_out);
 
   // Overwrites or creates an entry for |key|.
   // |entry| is the value to set, |now| is the current time
   // |ttl| is the "time to live".
   void Set(const Key& key,
            const Entry& entry,
            base::TimeTicks now,
            base::TimeDelta ttl);
 
   // Marks all entries as stale on account of a network change.
   void OnNetworkChange();
 
+  void set_eviction_callback(const EvictionCallback& callback) {
+    eviction_callback_ = callback;
+  }
+
   // Empties the cache
   void clear();
 
   // Returns the number of entries in the cache.
   size_t size() const;
 
   // Following are used by net_internals UI.
   size_t max_entries() const;
 
   const EntryMap& entries() const { return entries_; }
@@ skipping 25 matching lines @@
   // Returns true if this HostCache can contain no entries.
   bool caching_is_disabled() const { return max_entries_ == 0; }
 
   void EvictOneEntry(base::TimeTicks now);
 
   // Map from hostname (presumably in lowercase canonicalized format) to
   // a resolved result entry.
   EntryMap entries_;
   size_t max_entries_;
   int network_changes_;
+  EvictionCallback eviction_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(HostCache);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_HOST_CACHE_H_