Handles created inside each loop iteration should be freed as the
current iteration goes out of scope.

TBR=yangguo@chromium.org

Bug: v8:7122, chromium:763839
Change-Id: I70a95457c773b26792d87734dab62bc8f4f5fbd0
Reviewed-on: https://chromium-review.googlesource.com/796794Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49737}