Split out RtcpCnameCallback from RtcpStatisticsCallback

Cname callback is used only on receive side, and statistics (soon)
only on the send side.

Bug: webrtc:10679
Change-Id: I122e9cafaea93cd0ba75dc955a652d9d4bddc379
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/147867
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28767}

modules/rtp_rtcp/include/rtcp_statistics.h

@@ -13,6 +13,8 @@
 
 #include <stdint.h>
 
+#include "absl/strings/string_view.h"
+
 namespace webrtc {
 
 // Statistics for an RTCP channel
@@ -29,7 +31,6 @@ class RtcpStatisticsCallback {
 
   virtual void StatisticsUpdated(const RtcpStatistics& statistics,
                                  uint32_t ssrc) = 0;
-  virtual void CNameChanged(const char* cname, uint32_t ssrc) = 0;
 };
 
 // Statistics for RTCP packet types.
@@ -98,5 +99,13 @@ class RtcpPacketTypeCounterObserver {
       const RtcpPacketTypeCounter& packet_counter) = 0;
 };
 
+// Invoked for each cname passed in RTCP SDES blocks.
+class RtcpCnameCallback {
+ public:
+  virtual ~RtcpCnameCallback() = default;
+
+  virtual void OnCname(uint32_t ssrc, absl::string_view cname) = 0;
+};
+
 }  // namespace webrtc
 #endif  // MODULES_RTP_RTCP_INCLUDE_RTCP_STATISTICS_H_