Revert "Remove early bail-out in VisitWeakList to investigate chrasher."

>  BUG=468601
>  LOG=n
>
>  Review URL: https://codereview.chromium.org/1016353002
>
>  Cr-Commit-Position: refs/heads/master@{#27317}

R=hpayer@chromium.org
BUG=v8:3996,chromium:468601
LOG=n

Review URL: https://codereview.chromium.org/1080303002

Cr-Commit-Position: refs/heads/master@{#27814}