The embedders should use the new EmbedderGraph API to provide retainer
info.

Bug: chromium:749490
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: Iac8dc1e749ef14277b027f43e799357c5bd413ea
Reviewed-on: https://chromium-review.googlesource.com/948489
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52059}