This makes the dependency graph simpler and prepares for moving the
unit classes to api/.
Bug: webrtc:9155
Change-Id: I1b36d5e05f75d70ba8951e880d76359f896f7741
Reviewed-on: https://webrtc-review.googlesource.com/74920
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23161}