Add an implementation for async_network_alive to Linux

chrome/browser/sync/engine/syncapi.cc

 // Copyright (c) 2006-2009 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/engine/syncapi.h"
 
 #include "build/build_config.h"
 
 #if defined(OS_WIN)
 #include <windows.h>
@@ skipping 232 matching lines @@
       if (result < 0) {
         LOG(ERROR) << "select() returned unexpected result " << result;
         break;
       }
 
       // If exit_pipe was written to, we're done.
       if (FD_ISSET(params_->exit_pipe[0], &rdfs)) {
         break;
       }
 
-      // If result is 0, select timed out.
+      // If fd is set, the network address might have changed.
       if (FD_ISSET(fd, &rdfs)) {
         char buf[4096];
         struct iovec iov = { buf, sizeof(buf) };
         struct sockaddr_nl sa;
 
         struct msghdr msg = { (void *)&sa, sizeof(sa), &iov, 1, NULL, 0, 0 };
         recvmsg(fd, &msg, 0);
 
         params_->conn_mgr->CheckServerReachable();
       } else {
@@ skipping 1431 matching lines @@
 BaseTransaction::~BaseTransaction() {
   delete lookup_;
 }
 
 UserShare* SyncManager::GetUserShare() const {
   DCHECK(data_->initialized()) << "GetUserShare requires initialization!";
   return data_->GetUserShare();
 }
 
 }  // namespace sync_api