Speculative (2) Windows fix

Change-Id: Ibaf7618dc89368ded029001b7a9ad2242d1954a6
diff --git a/include/perfetto/base/file_utils.h b/include/perfetto/base/file_utils.h
index b2cfbe2..1efb450 100644
--- a/include/perfetto/base/file_utils.h
+++ b/include/perfetto/base/file_utils.h
@@ -17,6 +17,8 @@
 #ifndef INCLUDE_PERFETTO_BASE_FILE_UTILS_H_
 #define INCLUDE_PERFETTO_BASE_FILE_UTILS_H_
 
+#include <stddef.h>
+
 #include <string>
 
 namespace perfetto {