The default value for optional object structure members wasn't set
correctly for C++ structures.
Bug: dawn:22
Change-Id: I09e7f3675f6e0b5990ddcf03601b3b91cd25f553
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/31200
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Shaobo Yan <shaobo.yan@intel.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>