We want to replace all uses of CallOnForegroundThread eventually by the
new TaskRunner API so that we can eventually deprecate the old API and
remove it.

R=leszeks@chromium.org

Bug: v8:8238
Change-Id: I6a1e55fe431225ffe4c77cd3387f3b060eb43edf
Reviewed-on: https://chromium-review.googlesource.com/c/1256866Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56375}