The code for the initialization of the wrapper promise was using the
generic InitializeJSObjectFromMap() helper, which generates a loop to
initialization all fields of some generic object. In this particular
case we're constructing a JSPromise, so we only need to initialize the
elements and properties pointers, since all the other fields are taken
care of by the PromiseInit() call on the next line anyways.

Bug: v8:7253, v8:8238
Change-Id: If11963d1f94607ed9e48788f597c81c7344aafbe
Reviewed-on: https://chromium-review.googlesource.com/c/1281602Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56665}