As far as I can see, we have had this bug as long as destructuring assignments
have been there (i.e., this is not regression).

The problem was that Parser::DoParseFunction parsed the arrow function parameters
but didn't rewrite the destructuring assignments in them.

BUG=chromium:704811

Change-Id: I0b1424e7d5103eda6efd51b403fe81a4ee235e01
Reviewed-on: https://chromium-review.googlesource.com/459618
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44177}