Align the library with the current blink implementation.
TraceStrongly takes a WeakMember and strongifies it so that the
referenced objects is retained.
This is used in blink during tracing of some weak collections.

Bug: chromium:1056170
Change-Id: I306f84fc37a856d309bccc7f544750abb2bdc7c9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2479003
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Auto-Submit: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70561}