Enbedders should switch to EmbedderHeapTracer API.

BUG=v8:5828

Change-Id: I82f2bc583d246617865a17f5904e02cd35f92fec
Reviewed-on: https://chromium-review.googlesource.com/448539Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43551}