Revert of Adding "first packet received" notification to PeerConnectionObserver.

talk/app/webrtc/peerconnection.h

 /*
  * libjingle
  * Copyright 2012 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
  *
  *  1. Redistributions of source code must retain the above copyright notice,
  *     this list of conditions and the following disclaimer.
  *  2. Redistributions in binary form must reproduce the above copyright notice,
@@ skipping 308 matching lines @@
 
   // Notifications from WebRtcSession relating to BaseChannels.
   void OnVoiceChannelDestroyed();
   void OnVideoChannelDestroyed();
   void OnDataChannelCreated();
   void OnDataChannelDestroyed();
   // Called when the cricket::DataChannel receives a message indicating that a
   // webrtc::DataChannel should be opened.
   void OnDataChannelOpenMessage(const std::string& label,
                                 const InternalDataChannelInit& config);
-  void OnFirstMediaPacketReceived();
 
   RtpSenderInterface* FindSenderById(const std::string& id);
 
   std::vector<rtc::scoped_refptr<RtpSenderInterface>>::iterator
   FindSenderForTrack(MediaStreamTrackInterface* track);
   std::vector<rtc::scoped_refptr<RtpReceiverInterface>>::iterator
   FindReceiverForTrack(MediaStreamTrackInterface* track);
 
   TrackInfos* GetRemoteTracks(cricket::MediaType media_type);
   TrackInfos* GetLocalTracks(cricket::MediaType media_type);
@@ skipping 52 matching lines @@
   // because its destruction fires signals (such as VoiceChannelDestroyed)
   // which will trigger some final actions in PeerConnection...
   rtc::scoped_ptr<WebRtcSession> session_;
   // ... But stats_ depends on session_ so it should be destroyed even earlier.
   rtc::scoped_ptr<StatsCollector> stats_;
 };
 
 }  // namespace webrtc
 
 #endif  // TALK_APP_WEBRTC_PEERCONNECTION_H_