Reland of [compiler] Make feedback vector cope with flag changes. (patchset #1 id:1 of https://codereview.chromium.org/1876103002/ )

Reason for revert:
Did not fail on another roll including this CL ..

Original issue's description:
> Revert of [compiler] Make feedback vector cope with flag changes. (patchset #1 id:1 of https://codereview.chromium.org/1869693003/ )
>
> Reason for revert:
> Blocks current roll: https://codereview.chromium.org/1876713002/ according to bisect: https://codereview.chromium.org/1872353002/#ps80001
>
> Original issue's description:
> > [compiler] Make feedback vector cope with flag changes.
> >
> > This fixes corner cases where the layout of feedback vectors baked into
> > the snapshot is different from the expected layout, depending on some
> > runtime flags. We make sure the feedback vector is regenereated for
> > functions that are not compiled. Flag changes of this kind are only
> > allowed when code is not serialized.
> >
> > An alternative solution would be to not serialize the feedback vector
> > for such cases in the first place. That solution however would have a
> > higher overhead, as it would required the serializer to be able to
> > recognize feedback vectors while generating a snapshot.
> >
> > R=mvstanton@chromium.org
> > TEST=mjsunit/regress/regress-crbug-600995
> > BUG=chromium:600995
> > LOG=n
> >
> > Committed: https://crrev.com/460bff5fb6af2bd79e610f89afdf6da9dba3cf0c
> > Cr-Commit-Position: refs/heads/master@{#35339}
>
> TBR=mvstanton@chromium.org,mstarzinger@chromium.org
>
> BUG=chromium:600995
> LOG=N
> NOTRY=true
>
> Committed: https://crrev.com/78049e9c4837f053575d6c71e53ae12fec99f1aa
> Cr-Commit-Position: refs/heads/master@{#35392}

TBR=mvstanton@chromium.org,mstarzinger@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:600995

Review URL: https://codereview.chromium.org/1876973002

Cr-Commit-Position: refs/heads/master@{#35398}