This internalization was not necessary, since the rewriting does not use
the .result name string.

The subsequent internalization is still needed, so to simplify later
refactoring, this CL also adds "releasing" of the disallow scopes and
uses them here immediately before the second internalize. Notably, this
means that the rewriting is now also in the disallow scopes.

Driveby: Remove isolate from the rewriter's processor constructor.

BUG=v8:5832

Review-Url: https://codereview.chromium.org/2635913002
Cr-Commit-Position: refs/heads/master@{#42403}