This reverts commit b2d1f272.

Reason for revert: assertion failure

Original change's description:
> [heap, runtime] Fix data race in prototype map transition during
> concurrent marking.
> 
> BUG=chromium:694255
> 
> Change-Id: I172167623e9deab692fb506d7d4211d210b09a80
> Reviewed-on: https://chromium-review.googlesource.com/579092
> Reviewed-by: Igor Sheludko <ishell@chromium.org>
> Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#46813}

TBR=ulan@chromium.org,ishell@chromium.org

Change-Id: Ida5c66c3e880b9a03ffacbc6f32b1d5b2cfc8260
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:694255
Reviewed-on: https://chromium-review.googlesource.com/581287Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46815}