Revert "Merge to master: contention over isolate data slots"

Reason for revert: embeddertests failed.
This reverts commit 70bc04b16646c92f221c5aa56831b01d6ec7c1ca.

TBR=thestig@chromium.org

Review URL: https://codereview.chromium.org/1358263004 .
3 files changed