Fix missing include that causes Skia builds to fail

One of the issues blocking Dawn->Skia rolls

Change-Id: Ia3c68edd2c2745586dfb6a778e3a493df20aa66d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/35820
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
Auto-Submit: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>

src/common/ityp_array.h

diff --git a/src/common/ityp_array.h b/src/common/ityp_array.h
index 48e080f..0544de9 100644
--- a/src/common/ityp_array.h
+++ b/src/common/ityp_array.h
@@ -19,6 +19,7 @@
 #include "common/UnderlyingType.h"
 
 #include <array>
+#include <cstddef>
 #include <type_traits>
 
 namespace ityp {