- When a global object changes, invalidate its validity cell.
- The global object prototypes don't need to be gathered into an array in InitPrototypeChecks.

Bug: v8:7159
Change-Id: I3621c914d08b83e49e8a391800a92eb53ba19feb
Reviewed-on: https://chromium-review.googlesource.com/808588Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49901}