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}
