- rewritten couple tests,
- migrated JSMessageObject to real Script instead of wrapper,
- removed wrapper.

R=yangguo@chromium.org
TBR=ulan@chromium.org

Bug: v8:5530
Cq-Include-Trybots: luci.chromium.try:linux_chromium_headless_rel;luci.chromium.try:linux_chromium_rel_ng;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ia95492344c7b5978a940e2ab007b389384537148
Reviewed-on: https://chromium-review.googlesource.com/1112851Reviewed-by: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54274}