Some minifiers use the pattern !function ... () for JS code that should
be immediately executed. This change recognizes that pattern and treats
it equally to parenthesized functions.

A bit more background info is in the referenced bug.

R=verwaest@chromium.org
BUG=v8:5643

Review-Url: https://codereview.chromium.org/2509143003
Cr-Commit-Position: refs/heads/master@{#41114}