This places in the scaffolding for completely relying on the embedder
for these APIs. Once Chrome uses these instead of the old APIs,
we can cleanup further by removing the old callback insertion points
and not exposing the streaming APIs if callbacks aren't provided.

Bug: 
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I15abd257257be512674b18aa4af2e0a0153612a5
Reviewed-on: https://chromium-review.googlesource.com/520602
Commit-Queue: Brad Nelson <bradnelson@chromium.org>
Reviewed-by: Brad Nelson <bradnelson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45696}