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

net/base/dnsrr_resolver.cc

 // Copyright (c) 2010 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.
 
 #include "net/base/dnsrr_resolver.h"
 
 #if defined(OS_POSIX)
 #include <resolv.h>
 #endif
 
@@ skipping 146 matching lines @@
 #if defined(OS_POSIX)
 
   void Run() {
     // Runs on a worker thread.
 
     if (HandleTestCases()) {
       Finish();
       return;
     }
 
+    bool need_init = (_res.options & RES_INIT) == 0;
+#if WATCH_RESOLV_CONF
+    need_init |= ResolvConfUpdated();
+#endif
+
     bool r = true;
-    if ((_res.options & RES_INIT) == 0) {
+    if (need_init) {
+      LOG(INFO) << "Initializing resolver";
       if (res_ninit(&_res) != 0)
         r = false;
     }
 
     if (r) {
       unsigned long saved_options = _res.options;
       r = Do();
 
-#if defined(OS_POSIX) && !defined(OS_MACOSX) && !defined(OS_OPENBSD)
+#if WATCH_RESOLV_CONF
       if (!r && DnsReloadTimerHasExpired()) {
         // When there's no network connection, _res may not be initialized by
         // getaddrinfo. Therefore, we call res_nclose only when there are ns
         // entries.
         if (_res.nscount > 0)
           res_nclose(&_res);
         if (res_ninit(&_res) == 0)
           r = Do();
       }
 #endif
@@ skipping 546 matching lines @@
   inflight_.erase(j);
 
   job->HandleResult(result, response);
   delete job;
 }
 
 }  // namespace net
 
 DISABLE_RUNNABLE_METHOD_REFCOUNT(net::RRResolverHandle);
 DISABLE_RUNNABLE_METHOD_REFCOUNT(net::RRResolverWorker);