Print the object that is being destructured and update the error 
message.

Previously,
  d8> var [a] = {}
  (d8):1: TypeError: [Symbol.iterator] is not a function

Now,
  d8> var [a] = {}
  (d8):1: TypeError: {} is not iterable

Bug: v8:6513, v8:5532
Change-Id: I5cbfe7c7e20632bce1a48bd38a1b0c98d0ff0660
Reviewed-on: https://chromium-review.googlesource.com/557370
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Caitlin Potter <caitp@igalia.com>
Cr-Commit-Position: refs/heads/master@{#46457}