Expire but don't clear HostCache on DNS config change

net/base/network_change_notifier.cc

Index: net/base/network_change_notifier.cc
diff --git a/net/base/network_change_notifier.cc b/net/base/network_change_notifier.cc
index f5bfa8cbf5e281cdbd97f545fd3c8a7478078b3c..bd47e3ce9d7be82c04b38b19080562646382fd06 100644
--- a/net/base/network_change_notifier.cc
+++ b/net/base/network_change_notifier.cc
@@ -930,6 +930,12 @@ void NetworkChangeNotifier::NotifyObserversOfConnectionTypeChangeForTests(
 }
 
 // static
+void NetworkChangeNotifier::NotifyObserversOfDNSChangeForTests() {
+  if (g_network_change_notifier)
+    g_network_change_notifier->NotifyObserversOfDNSChangeImpl();
+}
+
+// static
 void NetworkChangeNotifier::NotifyObserversOfNetworkChangeForTests(
     ConnectionType type) {
   if (g_network_change_notifier)