Per https://tc39.github.io/ecma262/#sec-array.prototype.concat, step 6.

Bug: v8:6707, v8:6708
Change-Id: Iad3eb94a3b5fe35e5ecd1b8632612a7f2f169434
Reviewed-on: https://chromium-review.googlesource.com/636695
Commit-Queue: Adam Klein <adamk@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47654}