Reland of [parsing] Fix maybe-assigned for loop variables. (patchset #1 id:1 of https://codereview.chromium.org/2679263002/ )

Reason for revert:
False alarm, bot hiccup

Original issue's description:
> Revert of [parsing] Fix maybe-assigned for loop variables. (patchset #3 id:40001 of https://codereview.chromium.org/2673403003/ )
>
> Reason for revert:
> Speculative revert because of https://codereview.chromium.org/2679163002/.
>
> Original issue's description:
> > [parsing] Fix maybe-assigned for loop variables.
> >
> > Due to hoisting, the value of a 'var'-declared variable may actually change even
> > if the code contains only the "initial" assignment, namely when that assignment
> > occurs inside a loop.  For example:
> >
> >   let i = 10;
> >   do { var x = i } while (i--):
> >
> > As a simple and very conservative approximation of this, we explicitly mark
> > as maybe-assigned any non-lexical variable whose "declaration" does not
> > syntactically occur in the function scope.  (In the example above, it
> > occurs in a block scope.)
> >
> > BUG=v8:5636
> >
> > Review-Url: https://codereview.chromium.org/2673403003
> > Cr-Commit-Position: refs/heads/master@{#42989}
> > Committed: https://chromium.googlesource.com/v8/v8/+/a33fcd663b28b8846e12b97c30d6e7d837767f86
>
> TBR=marja@chromium.org,adamk@chromium.org,neis@chromium.org
> # Skipping CQ checks because original CL landed less than 1 days ago.
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=v8:5636
>
> Review-Url: https://codereview.chromium.org/2679263002
> Cr-Commit-Position: refs/heads/master@{#43010}
> Committed: https://chromium.googlesource.com/v8/v8/+/f3ae5ccf57690d8c2d87c4fe1d10b103ad6a4ab3

TBR=marja@chromium.org,adamk@chromium.org,neis@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:5636

Review-Url: https://codereview.chromium.org/2686663002
Cr-Commit-Position: refs/heads/master@{#43013}