Instead of using a word to store the status of the promise, this
patch uses 2 bit on flags.

Bug: v8:5046
Change-Id: Ic651338230dbe1704c68de8652676f236a3298f0
Reviewed-on: https://chromium-review.googlesource.com/634623
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47628}