Revert of Remove redundant ParseInfo::scope_. (patchset #4 id:60001 of https://codereview.chromium.org/2216563003/ )

Reason for revert:
Reverting to revert https://codereview.chromium.org/2209573002

Original issue's description:
> Remove redundant ParseInfo::scope_.
>
> This was always set to the literal's scope.
>
> (Additional change: mark getters as const.)
>
> R=adamk@chromium.org
> BUG=
>
> Committed: https://crrev.com/23ea0782977ed3a4dd113462af9ecbfd6ff0ce94
> Cr-Commit-Position: refs/heads/master@{#38372}

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

Review-Url: https://codereview.chromium.org/2222503002
Cr-Commit-Position: refs/heads/master@{#38379}