Fix compilation with GCC on size_t wihtout #include <cstddef>

Change-Id: I78afc46e1b931a9faf6efc6592abdc6a14a2218b
diff --git a/src/tracing/core/id_allocator.h b/src/tracing/core/id_allocator.h
index 90df970..97c9981 100644
--- a/src/tracing/core/id_allocator.h
+++ b/src/tracing/core/id_allocator.h
@@ -19,6 +19,7 @@
 
 #include <stdint.h>
 
+#include <cstddef>
 #include <type_traits>
 #include <vector>