Update from https://crrev.com/306655

sandbox/linux/services/thread_helpers.cc

 // Copyright 2014 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 "sandbox/linux/services/thread_helpers.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <signal.h>
 #include <sys/types.h>
@@ skipping 25 matching lines @@
   // determining if the current proces is monothreaded it works: if at any
   // time it becomes monothreaded, it'll stay so.
   return task_stat.st_nlink == 3;
 }
 
 }  // namespace
 
 bool ThreadHelpers::IsSingleThreaded(int proc_self_task) {
   DCHECK_LE(-1, proc_self_task);
   if (-1 == proc_self_task) {
-    const int task_fd = open("/proc/self/task/", O_RDONLY | O_DIRECTORY);
+    const int task_fd =
+        open("/proc/self/task/", O_RDONLY | O_DIRECTORY | O_CLOEXEC);
     PCHECK(0 <= task_fd);
     const bool result = IsSingleThreadedImpl(task_fd);
     PCHECK(0 == IGNORE_EINTR(close(task_fd)));
     return result;
   } else {
     return IsSingleThreadedImpl(proc_self_task);
   }
 }
 
 bool ThreadHelpers::StopThreadAndWatchProcFS(int proc_self_task,
@@ skipping 36 matching lines @@
     // In practice, this never goes through more than a couple iterations. In
     // debug mode, crash after 64ms (+ eventually 25 times the granularity of
     // the clock) in nanosleep(2).
     DCHECK_GT(25U, iterations);
   }
 
   return true;
 }
 
 }  // namespace sandbox