Fix to only call DnsConfigService::WatchConfig() once

This was an accidental bug introduced in r659155 that only happens in the
weird cases where NetworkChangeNotifierWin fails to watch for address
changes.

Bug: 967297
Change-Id: Ic4a575599be4ae4e150f19f672cf07aa82376e83
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1632449
Auto-Submit: Paul Jensen <pauljensen@chromium.org>
Commit-Queue: Eric Orth <ericorth@chromium.org>
Reviewed-by: Eric Orth <ericorth@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663960}

net/base/network_change_notifier_win.cc

@@ -294,11 +294,14 @@ void NetworkChangeNotifierWin::WatchForAddressChange() {
 bool NetworkChangeNotifierWin::WatchForAddressChangeInternal() {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 
+  if (!posted_watch_config_) {
+    posted_watch_config_ = true;
     dns_config_service_runner_->PostTask(
         FROM_HERE, base::BindOnce(&DnsConfigService::WatchConfig,
                                   base::Unretained(dns_config_service_.get()),
                                   base::BindRepeating(
                                       &NetworkChangeNotifier::SetDnsConfig)));
+  }
 
   ResetEventIfSignaled(addr_overlapped_.hEvent);
   HANDLE handle = nullptr;

net/base/network_change_notifier_win.h

@@ -124,6 +124,9 @@ class NET_EXPORT_PRIVATE NetworkChangeNotifierWin
   // Number of times polled to check if still offline.
   int offline_polls_;
 
+  // Keeps track of whether DnsConfigService::WatchConfig() has been called.
+  bool posted_watch_config_ = false;
+
   SEQUENCE_CHECKER(sequence_checker_);
 
   // Used for calling WatchForAddressChange again on failure.