so that it can be shared between different packetizers and thus easier to extend Bug: webrtc:9680 Change-Id: Ie5e904ad27afb8dd2ed35ef9e009f7f408017b2f Reviewed-on: https://webrtc-review.googlesource.com/97661 Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org> Commit-Queue: Danil Chapovalov <danilchap@webrtc.org> Cr-Commit-Position: refs/heads/master@{#24555}