The embedders should use the EmbedderGraph API. The similar structure
can be created with the following steps:
1) Create a root node for each retainer info group.
2) Iterate all handles using Isolate::VisitHandlesWithClassIds.
3) Add an edge from the retainer info node to the v8 wrapper node.
4) Add an edge from the v8 wrapper node to the retainer info node.

See how HeapSnapshotRetainedObjectInfo is converted to the new API.

Bug: chromium:749490
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
Change-Id: I124ae3853354863b4f888e6aa2ea13777dcaa37d
Reviewed-on: https://chromium-review.googlesource.com/948842
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52067}