Implement host-based deletion for the hostname resolution cache.

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 7b3d350a8f8c624509f0906980a55756f7d1ef40..ccda0eb9a926e9da52402743e32071e0de4b1b7f 100644
--- a/net/dns/host_cache.h
+++ b/net/dns/host_cache.h
@@ -146,9 +146,13 @@ class NET_EXPORT HostCache : NON_EXPORTED_BASE(public base::NonThreadSafe) {
     eviction_callback_ = callback;
   }
 
-  // Empties the cache
+  // Empties the cache.
   void clear();
 
+  // Clears hosts matching |host_filter| from the cache.
+  void ClearForHosts(
+      const base::Callback<bool(const std::string&)>& host_filter);
+
   // Returns the number of entries in the cache.
   size_t size() const;