Switch to standard integer types in sandbox/.

sandbox/linux/integration_tests/namespace_unix_domain_socket_unittest.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 <sched.h>
+#include <stddef.h>
 #include <stdio.h>
 #include <string.h>
 #include <sys/socket.h>
 #include <sys/syscall.h>
 #include <sys/wait.h>
 #include <unistd.h>
 
 #include <utility>
 #include <vector>
 
@@ skipping 242 matching lines @@
 
   // Parent process.
   recv_sock.reset();
   SendHello(send_sock.get());
   WaitForExit(pid);
 }
 
 }  // namespace
 
 }  // namespace sandbox