Update from https://crrev.com/306655

sandbox/linux/services/proc_util.h

+// 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.
+
+#ifndef SANDBOX_LINUX_SERVICES_PROC_UTIL_H_
+#define SANDBOX_LINUX_SERVICES_PROC_UTIL_H_
+
+#include "base/macros.h"
+#include "sandbox/sandbox_export.h"
+
+namespace sandbox {
+
+class SANDBOX_EXPORT ProcUtil {
+ public:
+  // Returns the number of file descriptors in the current process's FD
+  // table, excluding |proc_fd|, which should be a file descriptor for
+  // /proc.
+  static int CountOpenFds(int proc_fd);
+
+  // Checks whether the current process has any directory file descriptor open.
+  // Directory file descriptors are "capabilities" that would let a process use
+  // system calls such as openat() to bypass restrictions such as
+  // DropFileSystemAccess().
+  // Sometimes it's useful to call HasOpenDirectory() after file system access
+  // has been dropped. In this case, |proc_fd| should be a file descriptor to
+  // /proc. The file descriptor in |proc_fd| will be ignored by
+  // HasOpenDirectory() and remains owned by the caller. It is very important
+  // for the caller to close it.
+  // If /proc is available, |proc_fd| can be passed as -1.
+  // If |proc_fd| is -1 and /proc is not available, this function will return
+  // false.
+  static bool HasOpenDirectory(int proc_fd);
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(ProcUtil);
+};
+
+}  // namespace sandbox
+
+#endif  // SANDBOX_LINUX_SERVICES_PROC_UTIL_H_