The adder should be gotten before the iterator.

Motivation: Once this is done we should be able to use a for-of loop
instead which leads to cleaner code and correct behavior once the
for-of loop correctly supports abrupt completion.

BUG=None
LOG=N
R=adamk

Review URL: https://codereview.chromium.org/949933002

Cr-Commit-Position: refs/heads/master@{#26803}