Reland of move v8_toolset_for_d8 flag (patchset #2 id:80001 of https://codereview.chromium.org/1974773002/ )

Reason for revert:
Addressed link failure

Original issue's description:
> Revert of Remove v8_toolset_for_d8 flag (patchset #1 id:1 of https://codereview.chromium.org/1969793002/ )
>
> Reason for revert:
> blocks roll: https://codereview.chromium.org/1975753002/
>
> Original issue's description:
> > Remove v8_toolset_for_d8 flag
> >
> > R=machenbach@chromium.org
> > BUG=chromium:609107
> >
> > Committed: https://crrev.com/6cb38427984f3c31ff6c8813535cfd6ebf6058c4
> > Cr-Commit-Position: refs/heads/master@{#36198}
>
> TBR=machenbach@chromium.org,jochen@chromium.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=chromium:609107
>
> Committed: https://crrev.com/b33f9a6f24edef8447adcfb028b7f1d6e291c34e
> Cr-Commit-Position: refs/heads/master@{#36209}

TBR=machenbach@chromium.org,hablich@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=chromium:609107

Review-Url: https://codereview.chromium.org/1973363002
Cr-Commit-Position: refs/heads/master@{#36250}