Previously V8 created a promise to return to userland,
but instead we let the embedder create and track the promise.

Bug: v8:5785
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I8903ffbabf3a256f1c8df844a656a873da304586
Reviewed-on: https://chromium-review.googlesource.com/492646
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Daniel Clifford <danno@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46333}