test IWYU fixups for base

base/version.cc

 // 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.
 
 #include "base/version.h"
 
+#include <stddef.h>
+
 #include <algorithm>
 
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 
 namespace base {
 
 namespace {
@@ skipping 150 matching lines @@
   size_t count = components_.size();
   for (size_t i = 0; i < count - 1; ++i) {
     version_str.append(IntToString(components_[i]));
     version_str.append(".");
   }
   version_str.append(IntToString(components_[count - 1]));
   return version_str;
 }
 
 }  // namespace base