We execute the top-level function only to get to the wrapped function.
We could do the same by simply instantiating it.

Other approaches would change the parser so that the top-level function
is the wrapped function. However, that change violates existing scoping
invariants and fixing it would add a lot more complexity to the parser.

R=adamk@chromium.org, marja@chromium.org

Bug: v8:7172
Change-Id: I7272b8b58fc739d47a44da3a9d4a914af3e8cf3d
Reviewed-on: https://chromium-review.googlesource.com/836367Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50333}