This reverts commit d9d719e7.
Original review: https://codereview.chromium.org/2180273002/

With additional fixes to repair performance regressions:
- check PropertyCell::kValueOffset, not Cell::kValueOffset
- convert HeapNumbers to int on the fly if possible

NOPRESUBMIT=true

Review-Url: https://codereview.chromium.org/2227703003
Cr-Commit-Position: refs/heads/master@{#38497}