Calling clone(CLONE_NEWPID) results in the new pid namespace getting a new "init" process.

sandbox/linux/suid/init_process.h

Index: sandbox/linux/suid/init_process.h
===================================================================
--- sandbox/linux/suid/init_process.h	(revision 0)
+++ sandbox/linux/suid/init_process.h	(revision 0)
@@ -0,0 +1,11 @@
+// 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.
+
+#ifndef SANDBOX_LINUX_SUID_INIT_PROCESS_H_
+#define SANDBOX_LINUX_SUID_INIT_PROCESS_H_
+
+void SystemInitProcess(int init_fd, int child_pid, int proc_fd, int null_fd)
+  __attribute__((noreturn));
+
+#endif  // SANDBOX_LINUX_SUID_INIT_PROCESS_H_