Introduce JSCreateIterResultObject operator, as a way to optimize the
%_CreateIterResultObject intrinsic, which is used to provide uniform,
non-polymorphic result objects for iterators (and generators).  We
cannot utilize the existing JSCreate operator here, because there's no
constructor function for iterator result objects (as required by the
spec).

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/1531753002

Cr-Commit-Position: refs/heads/master@{#32901}