[net/dns] Watch configd notifications to detect DnsConfig changes on Mac.

net/dns/dns_config_service_posix.h

Index: net/dns/dns_config_service_posix.h
diff --git a/net/dns/dns_config_service_posix.h b/net/dns/dns_config_service_posix.h
index e266d0660025a1ee510eabd460d26c57ac08ff4e..cc26707b7e9ab24dfacdee86356b003cdb3f4c38 100644
--- a/net/dns/dns_config_service_posix.h
+++ b/net/dns/dns_config_service_posix.h
@@ -18,6 +18,7 @@
 namespace net {
 
 class FilePathWatcherWrapper;
+class NotifyWatcherMac;
 
 // Use DnsConfigService::CreateSystemService to use it outside of tests.
 namespace internal {
@@ -36,6 +37,9 @@ class NET_EXPORT_PRIVATE DnsConfigServicePosix
 
   scoped_ptr<FilePathWatcherWrapper> config_watcher_;
   scoped_ptr<FilePathWatcherWrapper> hosts_watcher_;
+#if defined(OS_MACOSX)
+  scoped_ptr<NotifyWatcherMac> notify_watcher_;
+#endif
 
   scoped_refptr<SerialWorker> config_reader_;
   scoped_refptr<SerialWorker> hosts_reader_;