GetHeapFromPayload returned the page header address instead of the
value of the first field of the header.

Bug: chromium:1056170
Change-Id: I4de5be975accced32460d6fab91543e6a5b07ba0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2143825
Auto-Submit: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67079}