Reland of SSRC and RSID may only refer to one sink each in RtpDemuxer

webrtc/call/rtp_demuxer.h

Index: webrtc/call/rtp_demuxer.h
diff --git a/webrtc/call/rtp_demuxer.h b/webrtc/call/rtp_demuxer.h
index e557c4dbcc0ab3978708c3a62a3062932da29657..dccf0b69a136f9581ed8b52992ffe04a7df39f61 100644
--- a/webrtc/call/rtp_demuxer.h
+++ b/webrtc/call/rtp_demuxer.h
@@ -31,18 +31,22 @@
   RtpDemuxer();
   ~RtpDemuxer();
 
-  // Registers a sink. The same sink can be registered for multiple ssrcs, and
-  // the same ssrc can have multiple sinks. Null pointer is not allowed.
-  void AddSink(uint32_t ssrc, RtpPacketSinkInterface* sink);
+  // Registers a sink. Multiple SSRCs may be mapped to the same sink, but
+  // each SSRC may only be mapped to one sink. The return value reports
+  // whether the association has been recorded or rejected. Rejection may occur
+  // if the SSRC has already been associated with a sink. The previously added
+  // sink is *not* forgotten.
+  bool AddSink(uint32_t ssrc, RtpPacketSinkInterface* sink);
 
-  // Registers a sink's association to an RSID. Null pointer is not allowed.
+  // Registers a sink's association to an RSID. Only one sink may be associated
+  // with a given RSID. Null pointer is not allowed.
   void AddSink(const std::string& rsid, RtpPacketSinkInterface* sink);
 
   // Removes a sink. Return value reports if anything was actually removed.
   // Null pointer is not allowed.
   bool RemoveSink(const RtpPacketSinkInterface* sink);
 
-  // Returns true if at least one matching sink was found.
+  // Handles RTP packets. Returns true if at least one matching sink was found.
   bool OnRtpPacket(const RtpPacketReceived& packet);
 
   // Allows other objects to be notified when RSID-SSRC associations are
@@ -53,12 +57,6 @@
   void DeregisterRsidResolutionObserver(const RsidResolutionObserver* observer);
 
  private:
-  // Records a sink<->SSRC association. This can happen by explicit
-  // configuration by AddSink(ssrc...), or by inferred configuration from an
-  // RSID-based configuration which is resolved to an SSRC upon
-  // packet reception.
-  void RecordSsrcToSinkAssociation(uint32_t ssrc, RtpPacketSinkInterface* sink);
-
   // Find the associations of RSID to SSRCs.
   void ResolveRsidToSsrcAssociations(const RtpPacketReceived& packet);
 
@@ -67,13 +65,13 @@
 
   // This records the association SSRCs to sinks. Other associations, such
   // as by RSID, also end up here once the RSID, etc., is resolved to an SSRC.
-  std::multimap<uint32_t, RtpPacketSinkInterface*> ssrc_sinks_;
+  std::map<uint32_t, RtpPacketSinkInterface*> ssrc_sinks_;
 
   // A sink may be associated with an RSID - RTP Stream ID. This tag has a
   // one-to-one association with an SSRC, but that SSRC is not yet known.
   // When it becomes known, the association of the sink to the RSID is deleted
   // from this container, and moved into |ssrc_sinks_|.
-  std::multimap<std::string, RtpPacketSinkInterface*> rsid_sinks_;
+  std::map<std::string, RtpPacketSinkInterface*> rsid_sinks_;
 
   // Observers which will be notified when an RSID association to an SSRC is
   // resolved by this object.