There are two reasons for Scopes to need information about eval calls
inside them:

  - Eval in a scope, or any of its inner scopes, turns off a bunch of
    scope analysis optimizations (e.g., all variables have to be treated
    as "used" and context-allocated).
  - Eval in a sloppy declaration scope means allows runtime addition
    of var declarations.

This patch aims to make the code better-reflect this reality.
It's meant as a pure cleanup, with no expected change in behavior.

Change-Id: I744c5051bb7a90b11420930e9596e5d6c35eb440
Reviewed-on: https://chromium-review.googlesource.com/602848
Commit-Queue: Adam Klein <adamk@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47257}