Resetting phantom handles while keeping finalizers alive leads to the
problem of eagerly resetting a handle although another finalizer keeps
it (transitively) alive.

This becomes a problem with internal pointers to Blink as without
global handle a Blink GC is free to collect wrappables.

This CL untangles finalizers handling from phantom handle resets by
introducing a separate path for resetting.

CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel

Bug: chromium:781728
Change-Id: Ica138b72942698fd996c6e9fe0bdc19cc432c010
Reviewed-on: https://chromium-review.googlesource.com/753724
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49162}