This prepares for future refactoring of rate controller. Bug: webrtc:9718 Change-Id: I425c8c547399bda98b4271a0d24a0bb7ee06bc13 Reviewed-on: https://webrtc-review.googlesource.com/c/112420 Commit-Queue: Sebastian Jansson <srte@webrtc.org> Reviewed-by: Björn Terelius <terelius@webrtc.org> Cr-Commit-Position: refs/heads/master@{#25846}