Take advantage of the HandleOrOffThreadHandle implicit conversions where
applicable.

Bug: chromium:1011762
Change-Id: Iaf49d9098368b402e1cd3d991629d3f5e718f28e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2046885
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66199}