This patch introduces assertPromiseFulfills and assertPromiseFulfills as
a replacement for assertPromiseResult because it’s more JavaScript-y.

BUG=v8:6921
R=ahaas@chromium.org

Also-By: ahaas@chromium.org
Change-Id: I2f865dba3992ddf3b58987bf0b376d143edb5c31
Reviewed-on: https://chromium-review.googlesource.com/718746
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48578}