DNS: Let requests specify a callback for future cache hits

net/dns/host_cache.h

Index: net/dns/host_cache.h
diff --git a/net/dns/host_cache.h b/net/dns/host_cache.h
index 700d5c2e8014322bc7e9c9bbb82977de5160dc6d..7b3d350a8f8c624509f0906980a55756f7d1ef40 100644
--- a/net/dns/host_cache.h
+++ b/net/dns/host_cache.h
@@ -113,6 +113,7 @@ class NET_EXPORT HostCache : NON_EXPORTED_BASE(public base::NonThreadSafe) {
   };
 
   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);
@@ -141,6 +142,10 @@ class NET_EXPORT HostCache : NON_EXPORTED_BASE(public base::NonThreadSafe) {
   // 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();
 
@@ -186,6 +191,7 @@ class NET_EXPORT HostCache : NON_EXPORTED_BASE(public base::NonThreadSafe) {
   EntryMap entries_;
   size_t max_entries_;
   int network_changes_;
+  EvictionCallback eviction_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(HostCache);
 };