Revert of Use VoiceChannel/VideoChannel directly from RtpSender/RtpReceiver. (patchset #3 id:40001 of https://codereview.webrtc.org/2046173002/ )

Reason for revert:
Broke peerconnection_unittest somehow, due to introduction of thread check. Will fix and reland.

Original issue's description:
> Use VoiceChannel/VideoChannel directly from RtpSender/RtpReceiver.
>
> This eliminates the need for the extra layer of indirection provided by
> mediastreamprovider.h. It will thus make it easier to implement new
> functionality in RtpSender/RtpReceiver.
>
> It also brings us one step closer to the end goal of combining "senders"
> and "send streams". Currently the sender still needs to go through the
> BaseChannel and MediaChannel, using an SSRC as a key.
>
> R=pthatcher@webrtc.org
>
> Committed: https://crrev.com/bc5831999d3354509d75357b659b4bb8e39f8a6c
> Cr-Commit-Position: refs/heads/master@{#13285}

TBR=pthatcher@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Review-Url: https://codereview.webrtc.org/2099843003
Cr-Commit-Position: refs/heads/master@{#13286}
diff --git a/webrtc/api/rtpreceiver.h b/webrtc/api/rtpreceiver.h
index 4b3bd4d..3b1fd92 100644
--- a/webrtc/api/rtpreceiver.h
+++ b/webrtc/api/rtpreceiver.h
@@ -10,21 +10,20 @@
 
 // This file contains classes that implement RtpReceiverInterface.
 // An RtpReceiver associates a MediaStreamTrackInterface with an underlying
-// transport (provided by cricket::VoiceChannel/cricket::VideoChannel)
+// transport (provided by AudioProviderInterface/VideoProviderInterface)
 
 #ifndef WEBRTC_API_RTPRECEIVER_H_
 #define WEBRTC_API_RTPRECEIVER_H_
 
 #include <string>
 
-#include "webrtc/api/mediastreaminterface.h"
+#include "webrtc/api/mediastreamprovider.h"
 #include "webrtc/api/rtpreceiverinterface.h"
 #include "webrtc/api/remoteaudiosource.h"
 #include "webrtc/api/videotracksource.h"
 #include "webrtc/base/basictypes.h"
 #include "webrtc/base/sigslot.h"
 #include "webrtc/media/base/videobroadcaster.h"
-#include "webrtc/pc/channel.h"
 
 namespace webrtc {
 
@@ -42,7 +41,7 @@
   AudioRtpReceiver(MediaStreamInterface* stream,
                    const std::string& track_id,
                    uint32_t ssrc,
-                   cricket::VoiceChannel* channel);
+                   AudioProviderInterface* provider);
 
   virtual ~AudioRtpReceiver();
 
@@ -61,10 +60,6 @@
     return track_.get();
   }
 
-  cricket::MediaType media_type() const override {
-    return cricket::MEDIA_TYPE_AUDIO;
-  }
-
   std::string id() const override { return id_; }
 
   RtpParameters GetParameters() const override;
@@ -75,21 +70,17 @@
 
   void SetObserver(RtpReceiverObserverInterface* observer) override;
 
-  // Does not take ownership.
-  // Should call SetChannel(nullptr) before |channel| is destroyed.
-  void SetChannel(cricket::VoiceChannel* channel);
+  cricket::MediaType media_type() override { return cricket::MEDIA_TYPE_AUDIO; }
 
  private:
   void Reconfigure();
-  void OnFirstPacketReceived(cricket::BaseChannel* channel);
+  void OnFirstAudioPacketReceived();
 
   const std::string id_;
   const uint32_t ssrc_;
-  cricket::VoiceChannel* channel_;
+  AudioProviderInterface* provider_;  // Set to null in Stop().
   const rtc::scoped_refptr<AudioTrackInterface> track_;
   bool cached_track_enabled_;
-  double cached_volume_ = 1;
-  bool stopped_ = false;
   RtpReceiverObserverInterface* observer_ = nullptr;
   bool received_first_packet_ = false;
 };
@@ -101,7 +92,7 @@
                    const std::string& track_id,
                    rtc::Thread* worker_thread,
                    uint32_t ssrc,
-                   cricket::VideoChannel* channel);
+                   VideoProviderInterface* provider);
 
   virtual ~VideoRtpReceiver();
 
@@ -114,10 +105,6 @@
     return track_.get();
   }
 
-  cricket::MediaType media_type() const override {
-    return cricket::MEDIA_TYPE_VIDEO;
-  }
-
   std::string id() const override { return id_; }
 
   RtpParameters GetParameters() const override;
@@ -128,16 +115,14 @@
 
   void SetObserver(RtpReceiverObserverInterface* observer) override;
 
-  // Does not take ownership.
-  // Should call SetChannel(nullptr) before |channel| is destroyed.
-  void SetChannel(cricket::VideoChannel* channel);
+  cricket::MediaType media_type() override { return cricket::MEDIA_TYPE_VIDEO; }
 
  private:
-  void OnFirstPacketReceived(cricket::BaseChannel* channel);
+  void OnFirstVideoPacketReceived();
 
   std::string id_;
   uint32_t ssrc_;
-  cricket::VideoChannel* channel_;
+  VideoProviderInterface* provider_;
   // |broadcaster_| is needed since the decoder can only handle one sink.
   // It might be better if the decoder can handle multiple sinks and consider
   // the VideoSinkWants.
@@ -146,7 +131,6 @@
   // the VideoRtpReceiver is stopped.
   rtc::scoped_refptr<VideoTrackSource> source_;
   rtc::scoped_refptr<VideoTrackInterface> track_;
-  bool stopped_ = false;
   RtpReceiverObserverInterface* observer_ = nullptr;
   bool received_first_packet_ = false;
 };