Revert 99677 (didn't help) - Revert 99666 (sync tests started failing on mac10.6:

net/base/network_change_notifier_linux.cc

Index: net/base/network_change_notifier_linux.cc
===================================================================
--- net/base/network_change_notifier_linux.cc	(revision 99692)
+++ net/base/network_change_notifier_linux.cc	(working copy)
@@ -7,19 +7,48 @@
 #include <errno.h>
 #include <sys/socket.h>
 
+#include "base/bind.h"
+#include "base/callback_old.h"
 #include "base/compiler_specific.h"
 #include "base/eintr_wrapper.h"
+#include "base/file_util.h"
+#include "base/files/file_path_watcher.h"
 #include "base/task.h"
 #include "base/threading/thread.h"
 #include "net/base/net_errors.h"
 #include "net/base/network_change_notifier_netlink_linux.h"
 
+using ::base::files::FilePathWatcher;
+
 namespace net {
 
 namespace {
 
 const int kInvalidSocket = -1;
 
+class DNSWatchDelegate : public FilePathWatcher::Delegate {
+ public:
+  explicit DNSWatchDelegate(Callback0::Type* callback)
+      : callback_(callback) {}
+  virtual ~DNSWatchDelegate() {}
+  // FilePathWatcher::Delegate interface
+  virtual void OnFilePathChanged(const FilePath& path) OVERRIDE;
+  virtual void OnFilePathError(const FilePath& path) OVERRIDE;
+ private:
+  scoped_ptr<Callback0::Type> callback_;
+  DISALLOW_COPY_AND_ASSIGN(DNSWatchDelegate);
+};
+
+void DNSWatchDelegate::OnFilePathChanged(const FilePath& path) {
+  // Calls NetworkChangeNotifier::NotifyObserversOfDNSChange().
+  if (callback_.get())
+    callback_->Run();
+}
+
+void DNSWatchDelegate::OnFilePathError(const FilePath& path) {
+  LOG(ERROR) << "DNSWatchDelegate::OnFilePathError for " << path.value();
+}
+
 }  // namespace
 
 class NetworkChangeNotifierLinux::Thread
@@ -42,6 +71,10 @@
     NetworkChangeNotifier::NotifyObserversOfIPAddressChange();
   }
 
+  void NotifyObserversOfDNSChange() {
+    NetworkChangeNotifier::NotifyObserversOfDNSChange();
+  }
+
   // Starts listening for netlink messages.  Also handles the messages if there
   // are any available on the netlink socket.
   void ListenForNotifications();
@@ -58,17 +91,36 @@
   // Technically only needed for ChromeOS, but it's ugly to #ifdef out.
   ScopedRunnableMethodFactory<Thread> method_factory_;
 
+  // Used to watch for changes to /etc/resolv.conf and /etc/hosts.
+  scoped_ptr<base::files::FilePathWatcher> resolv_file_watcher_;
+  scoped_ptr<base::files::FilePathWatcher> hosts_file_watcher_;
+  scoped_refptr<DNSWatchDelegate> file_watcher_delegate_;
+
   DISALLOW_COPY_AND_ASSIGN(Thread);
 };
 
 NetworkChangeNotifierLinux::Thread::Thread()
     : base::Thread("NetworkChangeNotifier"),
       netlink_fd_(kInvalidSocket),
-      ALLOW_THIS_IN_INITIALIZER_LIST(method_factory_(this)) {}
+      ALLOW_THIS_IN_INITIALIZER_LIST(method_factory_(this)) {
+}
 
 NetworkChangeNotifierLinux::Thread::~Thread() {}
 
 void NetworkChangeNotifierLinux::Thread::Init() {
+  resolv_file_watcher_.reset(new FilePathWatcher);
+  hosts_file_watcher_.reset(new FilePathWatcher);
+  file_watcher_delegate_ = new DNSWatchDelegate(NewCallback(this,
+      &NetworkChangeNotifierLinux::Thread::NotifyObserversOfDNSChange));
+  if (!resolv_file_watcher_->Watch(
+          FilePath(FILE_PATH_LITERAL("/etc/resolv.conf")),
+          file_watcher_delegate_.get())) {
+    LOG(ERROR) << "Failed to setup watch for /etc/resolv.conf";
+  }
+  if (!hosts_file_watcher_->Watch(FilePath(FILE_PATH_LITERAL("/etc/hosts")),
+          file_watcher_delegate_.get())) {
+    LOG(ERROR) << "Failed to setup watch for /etc/hosts";
+  }
   netlink_fd_ = InitializeNetlinkSocket();
   if (netlink_fd_ < 0) {
     netlink_fd_ = kInvalidSocket;
@@ -84,6 +136,10 @@
     netlink_fd_ = kInvalidSocket;
     netlink_watcher_.StopWatchingFileDescriptor();
   }
+  // Kill watchers early to make sure they won't try to call
+  // into us via the delegate during destruction.
+  resolv_file_watcher_.reset();
+  hosts_file_watcher_.reset();
 }
 
 void NetworkChangeNotifierLinux::Thread::OnFileCanReadWithoutBlocking(int fd) {