Add an implementation for async_network_alive to Linux

chrome/browser/sync/notifier/base/linux/network_status_detector_task_linux.cc

Index: chrome/browser/sync/notifier/base/linux/network_status_detector_task_linux.cc
===================================================================
--- chrome/browser/sync/notifier/base/linux/network_status_detector_task_linux.cc	(revision 37123)
+++ chrome/browser/sync/notifier/base/linux/network_status_detector_task_linux.cc	(working copy)
@@ -1,15 +0,0 @@
-// 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.
-
-#include "chrome/browser/sync/notifier/base/network_status_detector_task.h"
-
-namespace notifier {
-
-NetworkStatusDetectorTask* NetworkStatusDetectorTask::Create(
-    talk_base::Task* parent) {
-  // TODO(sync): No implementation for linux.
-  return NULL;
-}
-
-}  // namespace notifier