iwyu: Cleanup in the following files:

base/command_line.h

 // Copyright (c) 2011 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.
 
 // This class works with command lines: building and parsing.
 // Switches can optionally have a value attached using an equals sign, as in
 // "-switch=value". Arguments that aren't prefixed with a switch prefix are
 // saved as extra arguments. An argument of "--" will terminate switch parsing,
 // causing everything after to be considered as extra arguments.
 
 // There is a singleton read-only CommandLine that represents the command line
 // that the current process was started with.  It must be initialized in main().
 
 #ifndef BASE_COMMAND_LINE_H_
 #define BASE_COMMAND_LINE_H_
 #pragma once
 
+#include <stddef.h>
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/base_api.h"
-#include "base/basictypes.h"
 #include "build/build_config.h"
 
 class FilePath;
 
 class BASE_API CommandLine {
  public:
 #if defined(OS_WIN)
   // The native command line string type.
   typedef std::wstring StringType;
 #elif defined(OS_POSIX)
@@ skipping 140 matching lines @@
   // Non-switch command line arguments.
   StringVector args_;
 
   // Allow the copy constructor. A common pattern is to copy the current
   // process's command line and then add some flags to it. For example:
   //   CommandLine cl(*CommandLine::ForCurrentProcess());
   //   cl.AppendSwitch(...);
 };
 
 #endif  // BASE_COMMAND_LINE_H_