Revert of Remove AudioTrackRenderer

talk/media/base/audiorenderer.h

Index: talk/media/base/audiorenderer.h
diff --git a/talk/media/base/audiorenderer.h b/talk/media/base/audiorenderer.h
index 229c36e8b1eccfb57b042ef643fe1c3f232ddaae..5c03576fa79d2a593a2013b23035020fe4d1f852 100644
--- a/talk/media/base/audiorenderer.h
+++ b/talk/media/base/audiorenderer.h
@@ -55,6 +55,20 @@
   // to the renderer at a time.
   virtual void SetSink(Sink* sink) {}
 
+  // Add the WebRtc VoE channel to the renderer.
+  // For local stream, multiple WebRtc VoE channels can be connected to the
+  // renderer. While for remote stream, only one WebRtc VoE channel can be
+  // connected to the renderer.
+  // TODO(xians): Remove this interface after Chrome switches to the
+  // AudioRenderer::Sink interface.
+  virtual void AddChannel(int channel_id) {}
+
+  // Remove the WebRtc VoE channel from the renderer.
+  // This method is called when the VoE channel is going away.
+  // TODO(xians): Remove this interface after Chrome switches to the
+  // AudioRenderer::Sink interface.
+  virtual void RemoveChannel(int channel_id) {}
+
  protected:
   virtual ~AudioRenderer() {}
 };