Rectify our use of std::nullptr_t, inclusions of <stddef.h>/<cstddef>.

mojo/edk/util/command_line.h

 // Copyright 2015 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.
 
 // Provides a simple class, |CommandLine|, for dealing with command lines (and
 // flags and positional arguments).
 //
 // * Options (a.k.a. flags or switches) are all of the form "--name=<value>" (or
 //   "--name", but this is indistinguishable from "--name="), where <value> is a
 //   string. Not supported: "-name", "-n", "--name <value>", "-n <value>", etc.
@@ skipping 18 matching lines @@
 // not being able to distinguish "no value" from "empty value").
 //
 // [*] This is somewhat annoying for users, but: a. it's standard Unix behavior
 // for most command line parsers, b. it makes "my_program *" (etc.) safer (which
 // mostly explains a.), c. it makes parsing "subcommands", like "my_program
 // --flag_for_my_program subcommand --flag_for_subcommand" saner.
 
 #ifndef MOJO_EDK_UTIL_COMMAND_LINE_H_
 #define MOJO_EDK_UTIL_COMMAND_LINE_H_
 
-#include <cstddef>
+#include <stddef.h>
+
 #include <initializer_list>
 #include <string>
 #include <unordered_map>
 #include <vector>
 
 #include "mojo/public/cpp/system/macros.h"
 
 namespace mojo {
 namespace util {
 
@@ skipping 165 matching lines @@
 
 // This is the "opposite" of the above factory functions, transforming a
 // |CommandLine| into a vector of argument strings according to the rules
 // outlined at the top of this file.
 std::vector<std::string> CommandLineToArgv(const CommandLine& command_line);
 
 }  // namespace util
 }  // namespace mojo
 
 #endif  // MOJO_EDK_UTIL_COMMAND_LINE_H_