Move some RTP-related observers from common_types.h

These classes moved to rtp_rtcp_defines.h:

  BitrateStatisticsObserver
  SendSideDelayObserver
  SendPacketObserver

Bug: webrtc:5876
Change-Id: I38861f8de555aff0b22e7a67a5ac0090a5e98d4e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/135464
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27870}

modules/rtp_rtcp/include/rtp_rtcp_defines.h

@@ -516,5 +516,36 @@ class RtcpAckObserver {
   virtual ~RtcpAckObserver() = default;
 };
 
+// Callback, used to notify an observer whenever new rates have been estimated.
+class BitrateStatisticsObserver {
+ public:
+  virtual ~BitrateStatisticsObserver() {}
+
+  virtual void Notify(uint32_t total_bitrate_bps,
+                      uint32_t retransmit_bitrate_bps,
+                      uint32_t ssrc) = 0;
+};
+
+// Callback, used to notify an observer whenever the send-side delay is updated.
+class SendSideDelayObserver {
+ public:
+  virtual ~SendSideDelayObserver() {}
+  virtual void SendSideDelayUpdated(int avg_delay_ms,
+                                    int max_delay_ms,
+                                    uint32_t ssrc) = 0;
+};
+
+// Callback, used to notify an observer whenever a packet is sent to the
+// transport.
+// TODO(asapersson): This class will remove the need for SendSideDelayObserver.
+// Remove SendSideDelayObserver once possible.
+class SendPacketObserver {
+ public:
+  virtual ~SendPacketObserver() {}
+  virtual void OnSendPacket(uint16_t packet_id,
+                            int64_t capture_time_ms,
+                            uint32_t ssrc) = 0;
+};
+
 }  // namespace webrtc
 #endif  // MODULES_RTP_RTCP_INCLUDE_RTP_RTCP_DEFINES_H_