DNS: Let requests specify a callback for future cache hits

net/dns/host_cache.cc

Index: net/dns/host_cache.cc
diff --git a/net/dns/host_cache.cc b/net/dns/host_cache.cc
index ee3d96215f35fc61c5c934bfe07f08e073345ced..7556e7eee478408afd182eef19360fafc3681ffe 100644
--- a/net/dns/host_cache.cc
+++ b/net/dns/host_cache.cc
@@ -234,6 +234,8 @@ void HostCache::EvictOneEntry(base::TimeTicks now) {
       oldest_it = it;
   }
 
+  if (!eviction_callback_.is_null())
+    eviction_callback_.Run(oldest_it->first, oldest_it->second);
   RecordErase(ERASE_EVICT, now, oldest_it->second);
   entries_.erase(oldest_it);
 }