Previously, we would first fire the PromiseRejectCallback before
fulfilling the promise. This patch changes the behavior to first
fulfill the promise. This behavior is more intuitive.

This patch also merges the check for PromiseHook callback with the
debug callback, since they use the same boolean bit on the isolate.

Bug: v8:6880
Change-Id: Ia04867e16423a1d6006f0f3f93a14fa6026e17ed
Reviewed-on: https://chromium-review.googlesource.com/700980
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48298}