The CompilationState should not be bound to a specific isolate. Hence
it cannot start foreground task. Instead, the callbacks themselves
should do this if they are specific to one Isolate.

R=mstarzinger@chromium.org

Bug: v8:8689, v8:8050
Change-Id: Ic86bba1dd645401b2b284a9f26eec87718b011e1
Reviewed-on: https://chromium-review.googlesource.com/c/1445977
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59225}