This changes RefCounted to increment and decrement the refcount by steps
of 2, so that a 1 bit payload can be inlined in the refcount. This
avoids using a whole boolean + padding (4 or 8 bytes in general) to know
if objects are errors.
Fixes a longstanding optimization TODO.
BUG=dawn:105
Change-Id: I5e8f66465d23772fb6082ea3e0d5d4aba2132648
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/13680
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>