We must close the iterator whenever the destructuring didn't exhaust it, unless an iterator operation (eg. next) threw.  We do this by wrapping the iterator use in a try-catch-finally similar to the desugaring of for-of.

This is behind --harmony-iterator-close.

R=adamk@chromium.org
BUG=v8:3566
LOG=Y

Review URL: https://codereview.chromium.org/1772793002

Cr-Commit-Position: refs/heads/master@{#34654}