... and use Smi Map::kPrototypeChainValid for the cases where direct receiver's
prototype is not JSObject instead of creating a new valid cell for each such
case. This will make a validity cell checking code simpler.

Bug: v8:5988
Change-Id: I52cf55797171cc8021d80e4e441615d0c8fc8bd4
Reviewed-on: https://chromium-review.googlesource.com/951384
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51803}