This will allow it to take an OffThreadIsolate in the future, without
requiring GetIsolate on SharedFunctionInfo.

Change-Id: I7db56d5f0587585f829b26e60683c133760d8ff1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2282534Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68696}