Fix missing Release() on RefBase::operator=(const T&).
Always acquire the new reference before dropping the existing reference.
Consider:
* Object A holds the only reference to object B.
* Ref of A is assigned B.
If A were released before referencing B, then B would be a dead pointer.
Remove RefBase::kNullValue, just use Traits::kNullValue. Avoids an unnecessary constexpr copy.
Add even more tests.
Change-Id: I111079d56cbf8c09162aa6e493078bead9ae97fa
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/55882
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Commit-Queue: Ben Clayton <bclayton@google.com>
