This is a reland of 25207bf8

Original change's description:
> Remove isolate.h include from external-reference.h
>
> This triggers a bunch of other necessary include tweaks for files that
> used to work until now because they indirectly included isolate.h
> through external-reference.h.
>
> Bug: v8:6666
> Change-Id: I8d48db44dcc321fa32a6279f3ddacb41ab58f975
> Reviewed-on: https://chromium-review.googlesource.com/972042
> Commit-Queue: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Peter Marshall <petermarshall@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52103}

TBR=petermarshall@chromium.org

Bug: v8:6666
Change-Id: Ibbcf2c116dc3b202d325fd7644e8755ffe583ef1
Reviewed-on: https://chromium-review.googlesource.com/973062Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52108}