I'm also changing the function signature to take the descriptor_index
instead of the FieldIndex, because this lets me reuse the vector of
property descriptors as storage.

Bug: v8:7790
Change-Id: Ie9dadcba2204b6825e5791f9c630fc8b1079a930
Reviewed-on: https://chromium-review.googlesource.com/1227873
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55981}