Persistent handles are always independent these days. Users should mark
weak handles as active using MarkActive if they want to keep weak
handles that are otherwise unreachable alive across scavenges.

Bug: chromium:780749
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I116e984ce14a035d1cef491d49f11a388fa8169d
Reviewed-on: https://chromium-review.googlesource.com/759794
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49456}