iwyu: Cleanup in the following files:

base/file_path.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.
 
 // FilePath is a container for pathnames stored in a platform's native string
 // type, providing containers for manipulation in according with the
 // platform's conventions for pathnames.  It supports the following path
 // types:
 //
 //                   POSIX            Windows
@@ skipping 82 matching lines @@
 //    FilePath treats c://, c:\\, //, and \\ all equivalently.
 //    Reference:
 //    The Old New Thing, "Why is a drive letter permitted in front of UNC
 //    paths (sometimes)?", available at:
 //    http://blogs.msdn.com/oldnewthing/archive/2005/11/22/495740.aspx
 
 #ifndef BASE_FILE_PATH_H_
 #define BASE_FILE_PATH_H_
 #pragma once
 
+#include <stddef.h>
 #include <string>
 #include <vector>
 
 #include "base/base_api.h"
-#include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/hash_tables.h"
+#include "base/string16.h"
 #include "base/string_piece.h"  // For implicit conversions.
+#include "build/build_config.h"
 
 // Windows-style drive letter support and pathname separator characters can be
 // enabled and disabled independently, to aid testing.  These #defines are
 // here so that the same setting can be used in both the implementation and
 // in the unit test.
 #if defined(OS_WIN)
 #define FILE_PATH_USES_DRIVE_LETTERS
 #define FILE_PATH_USES_WIN_SEPARATORS
 #endif  // OS_WIN
 
@@ skipping 258 matching lines @@
 #define PRFilePathLiteral L"%ls"
 #endif  // OS_WIN
 
 // Provide a hash function so that hash_sets and maps can contain FilePath
 // objects.
 #if defined(COMPILER_GCC)
 namespace __gnu_cxx {
 
 template<>
 struct hash<FilePath> {
-  std::size_t operator()(const FilePath& f) const {
+  size_t operator()(const FilePath& f) const {
     return hash<FilePath::StringType>()(f.value());
   }
 };
 
 }  // namespace __gnu_cxx
 #elif defined(COMPILER_MSVC)
 namespace stdext {
 
 inline size_t hash_value(const FilePath& f) {
   return hash_value(f.value());
 }
 
 }  // namespace stdext
 #endif  // COMPILER
 
 #endif  // BASE_FILE_PATH_H_