Use FileWatcher to watch system resolver config, on systems that require...

net/base/dns_reload_timer.h

 // Copyright (c) 2009 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_BASE_DNS_RELOAD_TIMER_H_
 #define NET_BASE_DNS_RELOAD_TIMER_H_
 #pragma once
 
 #include "build/build_config.h"
 
-#if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD)
+#define WATCH_RESOLV_CONF \
+        defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD)
+
+#if WATCH_RESOLV_CONF
+namespace base { class Thread; }
+
 namespace net {
 
 // DnsReloadTimerExpired tests the thread local DNS reload timer and, if it has
 // expired, returns true and resets the timer. See comments in
 // host_resolver_proc.cc for details.
 bool DnsReloadTimerHasExpired();
 
+// Returns true if a change to resolver configuration has been detected.
+bool ResolvConfUpdated();
+
+// Installs a FileWatch on system's resolver config (/etc/resolv.conf).
+// FileWatch has to run in file thread, so all this does is schedule a task to
+// run on file_thread.
+void InitResolvConfWatcher(base::Thread* file_thread);
+
 }  // namespace net
 #endif
 
 #endif  // NET_BASE_DNS_RELOAD_TIMER_H_