heap: Refactor API docs around pre-finalizers and eager sweeping

- Remove eager sweeping as the support will be dropped
- Extend pre-finalizer examples
- Clarify that pre-finalizers are not allowed to resurrect

Bug: 982754
Change-Id: Ia3a0a4bfa4c872d1eeacd568920ba5b820703828
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1697603
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676339}
1 file changed