The explicit state_ variable is used to prevent undefined behaviour
by double-joining the worker thread.

Bug: chromium:1276382
Change-Id: I338cfdb4a587eb57fec5a5a28b42371584c99102
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3318669Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78300}