Remove video_channel() from Session interface

remoting/protocol/video_writer.h

Index: remoting/protocol/video_writer.h
diff --git a/remoting/protocol/video_writer.h b/remoting/protocol/video_writer.h
index be4c715c01468b5c26323d6bed46a13a2d616362..1e0523e054a2e717955ba00e8a9ba6bb8214b8f6 100644
--- a/remoting/protocol/video_writer.h
+++ b/remoting/protocol/video_writer.h
@@ -11,6 +11,7 @@
 #define REMOTING_PROTOCOL_VIDEO_WRITER_H_
 
 #include "base/basictypes.h"
+#include "base/callback.h"
 #include "remoting/protocol/video_stub.h"
 
 namespace remoting {
@@ -23,10 +24,14 @@ class VideoWriter : public VideoStub {
  public:
   virtual ~VideoWriter();
 
+  // The callback is called when initialization is finished. The
+  // parameter is set to true on success.
+  typedef base::Callback<void(bool)> InitializedCallback;
+
   static VideoWriter* Create(const SessionConfig* config);
 
   // Initializes the writer.
-  virtual void Init(Session* session) = 0;
+  virtual void Init(Session* session, const InitializedCallback& callback) = 0;
 
   // Stops writing. Must be called on the network thread before this
   // object is destroyed.