This removes the need for Clone() so it is removed and also adds tests
for the new constructors.
BUG=dawn:11
Change-Id: Ia45c765c2d30e40b0e036427793a62327b2008fc
Reviewed-on: https://dawn-review.googlesource.com/c/1901
Reviewed-by: Stephen White <senorblanco@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>