Reland of Delete class SSRCDatabase, and its global ssrc registry.

webrtc/logging/rtc_event_log/rtc_event_log.proto

 syntax = "proto2";
 option optimize_for = LITE_RUNTIME;
 package webrtc.rtclog;
 
 enum MediaType {
   ANY = 0;
   AUDIO = 1;
   VIDEO = 2;
   DATA = 3;
 }
@@ skipping 84 matching lines @@
   optional bool incoming = 1;
 
   // required
   optional MediaType type = 2;
 
   // required - The whole packet including both payload and header.
   optional bytes packet_data = 3;
 }
 
 message AudioPlayoutEvent {
+  // TODO(ivoc): Rename, we currently use the "remote" ssrc, i.e. identifying
+  // the receive stream, while local_ssrc identifies the send stream, if any.
   // required - The SSRC of the audio stream associated with the playout event.
   optional uint32 local_ssrc = 2;
 }
 
 message BwePacketLossEvent {
   // required - Bandwidth estimate (in bps) after the update.
   optional int32 bitrate = 1;
 
   // required - Fraction of lost packets since last receiver report
   // computed as floor( 256 * (#lost_packets / #total_packets) ).
@@ skipping 147 matching lines @@
 
   // Whether forward error correction (FEC) is turned on or off.
   optional bool enable_fec = 4;
 
   // Whether discontinuous transmission (DTX) is turned on or off.
   optional bool enable_dtx = 5;
 
   // Number of audio channels that each encoded packet consists of.
   optional uint32 num_channels = 6;
 }