filter creates an output array with the Array species constructor for
storing values from the input array that pass the user-supplied
predicate function. Our new array builtins are implemented such that
if we fall out of the fast path, we'll pick up where we left off
in a continuation function. It's important to pass the index of
where we left off appending to the output array, because otherwise
we will read it at the start of the continuation function.

That would be observable, and a spec violation.

BUG=

Review-Url: https://codereview.chromium.org/2771483002
Cr-Commit-Position: refs/heads/master@{#44023}