[cros] RLZ tracking can be turned off via a flag file.

rlz/lib/recursive_cross_process_lock_posix.cc

 // Copyright (c) 2012 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 "rlz/lib/recursive_cross_process_lock_posix.h"
 
 #include <sys/file.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
+#include <unistd.h>
 
 #include "base/file_path.h"
 #include "base/logging.h"
 #include "base/posix/eintr_wrapper.h"
 
 namespace rlz_lib {
 
 bool RecursiveCrossProcessLock::TryGetCrossProcessLock(
     const FilePath& lock_filename) {
   bool just_got_lock = false;
@@ skipping 51 matching lines @@
     ignore_result(HANDLE_EINTR(flock(file_lock_, LOCK_UN)));
     ignore_result(HANDLE_EINTR(close(file_lock_)));
     file_lock_ = -1;
   }
 
   locking_thread_ = 0;
   pthread_mutex_unlock(&recursive_lock_);
 }
 
 }  // namespace rlz_lib