Fix header guards in //net.

net/dns/dns_config_watcher_mac.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#ifndef NET_DNS_DNS_CONFIG_WATCHER_MAC_H_
+#define NET_DNS_DNS_CONFIG_WATCHER_MAC_H_
+
 #include "base/callback_forward.h"
 #include "net/dns/dns_config_service_posix.h"
 #include "net/dns/notify_watcher_mac.h"
 
 namespace net {
 namespace internal {
 
 // Watches DNS configuration on Mac.
 class DnsConfigWatcher {
  public:
   bool Watch(const base::Callback<void(bool succeeded)>& callback);
 
   // Returns an error if the DNS configuration is invalid.
   // Returns CONFIG_PARSE_POSIX_OK otherwise.
   static ConfigParsePosixResult CheckDnsConfig();
 
  private:
   NotifyWatcherMac watcher_;
 };
 
 }  // namespace internal
 }  // namespace net
+
+#endif  // NET_DNS_DNS_CONFIG_WATCHER_MAC_H_