Embedders should use EmbedderHeapTracer::RegisterEmbedderReference
instead.

Bug: chromium:923361
Change-Id: If76c0354475798b09af95bedee0890594b29cd14
Reviewed-on: https://chromium-review.googlesource.com/c/1486472Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59840}