Makes it easier to write tests, and allows for moving rtp module ownership into the payload router in the future. The RtpPayloadParams class is split into declaration and definition and moved into separate files. Bug: webrtc:9517 Change-Id: I8700628edff19abcacfe8d3a20e4ba7476f712ad Reviewed-on: https://webrtc-review.googlesource.com/88564 Commit-Queue: Stefan Holmer <stefan@webrtc.org> Reviewed-by: Sebastian Jansson <srte@webrtc.org> Cr-Commit-Position: refs/heads/master@{#23983}