Adds missing includes for google3 roll.

Change-Id: Id99d168d3f127558179c7097af6575f07a260ed6
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/134465
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Loko Kung <lokokung@google.com>
Reviewed-by: Shrek Shao <shrekshao@google.com>
diff --git a/generator/templates/api_cpp_chained_struct.h b/generator/templates/api_cpp_chained_struct.h
index 59a0fd0..8c0af4a 100644
--- a/generator/templates/api_cpp_chained_struct.h
+++ b/generator/templates/api_cpp_chained_struct.h
@@ -20,6 +20,9 @@
 #ifndef {{API}}_CPP_CHAINED_STRUCT_H_
 #define {{API}}_CPP_CHAINED_STRUCT_H_
 
+#include <cstddef>
+#include <cstdint>
+
 // This header file declares the ChainedStruct structures separately from the {{metadata.api}}
 // headers so that dependencies can directly extend structures without including the larger header
 // which exposes capabilities that may require correctly set proc tables.