Let Stats class handle rtp timestamp to frame number mapping. Bug: none Change-Id: I2a29c89a25c75c4bbd6c6368a5d10514f90b3c42 Reviewed-on: https://webrtc-review.googlesource.com/41220 Commit-Queue: Åsa Persson <asapersson@webrtc.org> Reviewed-by: Sergey Silkin <ssilkin@webrtc.org> Reviewed-by: Rasmus Brandt <brandtr@webrtc.org> Cr-Commit-Position: refs/heads/master@{#21709}