This avoids generating different scopes on the two compilation passes, which
results in various delirious side-effects.

There's some cleanup to be done in lazy arrow function parsing, but I'd
rather do that in a separate patch, with this one targeted at fixing the
particular crash.

BUG=chromium:572589
LOG=n

Review URL: https://codereview.chromium.org/1575333004

Cr-Commit-Position: refs/heads/master@{#33311}