Switch to standard integer types in base/.

BUG=138542
[email protected]
NOPRESUBMIT=true

Review URL: https://codereview.chromium.org/1538743002

Cr-Commit-Position: refs/heads/master@{#366910}
diff --git a/base/lazy_instance_unittest.cc b/base/lazy_instance_unittest.cc
index ec9ef26..8947b129 100644
--- a/base/lazy_instance_unittest.cc
+++ b/base/lazy_instance_unittest.cc
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <stddef.h>
+
 #include "base/at_exit.h"
 #include "base/atomic_sequence_num.h"
 #include "base/lazy_instance.h"