Switch to standard integer types in extensions/.

BUG=138542
[email protected]

Review URL: https://codereview.chromium.org/1543053002

Cr-Commit-Position: refs/heads/master@{#366716}
diff --git a/extensions/renderer/module_system_test.cc b/extensions/renderer/module_system_test.cc
index 0db5495..68c4bd1 100644
--- a/extensions/renderer/module_system_test.cc
+++ b/extensions/renderer/module_system_test.cc
@@ -4,6 +4,8 @@
 
 #include "extensions/renderer/module_system_test.h"
 
+#include <stddef.h>
+
 #include <map>
 #include <string>
 #include <utility>