IIFE`s within a function are not guaranteed to be executed only once.
They can be called multiple times and compiler can inline them.
Do the one-shot optimizations only for IIFE`s from top-level code.

Bug: v8:8072, chromium:886580
Change-Id: I02370681cc3eab270edcc75ee120ca7ad768ed52
Reviewed-on: https://chromium-review.googlesource.com/1231174
Commit-Queue: Chandan Reddy <chandanreddy@google.com>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56024}