Also add tests for Object::SameValue.

R=jkummerow@chromium.org

Bug: v8:6791
Change-Id: I0611044dcfee4c6ba836629cf82d1589135e4ab0
Reviewed-on: https://chromium-review.googlesource.com/712034Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48486}