Implement video frame acknowledgements in the chromoting protocol.

remoting/protocol/video_stub.h

Index: remoting/protocol/video_stub.h
diff --git a/remoting/protocol/video_stub.h b/remoting/protocol/video_stub.h
index 59c231ea8403982000112429e0d91ebca77bf52f..548d3f5f6d027e9c9f258710093cb8cc465c8057 100644
--- a/remoting/protocol/video_stub.h
+++ b/remoting/protocol/video_stub.h
@@ -16,8 +16,22 @@ namespace protocol {
 
 class VideoStub {
  public:
-  virtual void ProcessVideoPacket(scoped_ptr<VideoPacket> video_packet,
-                                  const base::Closure& done) = 0;
+  // For each packet VideoStub calls the specified ProgressCallback to
+  // notify about packet progress. SENT state may be skipped, if the packet is
+  // processed locally. If SupportsAcks() returns true then DONE progress
+  // notification is emitted only after the acknowledgment has been received.
+  enum class PacketProgress {
+    SENT,

[Wez, 2015/02/03 00:54:32]

Do we really need the "SENT" state? It ends up making this API uglier - "sent"
has a reasonably specific meaning, whereas "done" is pretty generic, so it's not
clear why we need both.

[Sergey Ulanov, 2015/02/09 19:14:54]

Reverted this change now. Using VideoFeedbackStub instead.

+    DONE,
+  };
+  typedef base::Callback<void(PacketProgress progress)> ProgressCallback;
+
+  virtual void ProcessVideoPacket(
+      scoped_ptr<VideoPacket> video_packet,
+      const ProgressCallback& progress_callback) = 0;

[Wez, 2015/02/03 00:54:32]

This complicates the VideoStub interface quite a bit; the model I had in mind
for these stubs would have a VideoAckStub or VideoSendStatusStub (or some better
name;) through which these acknowledgements would be received by the sender,
without VideoStub implementations necessarily needing to know about that path -
would that do what you need here?

[Sergey Ulanov, 2015/02/09 19:14:54]

Reverted this change now. Using VideoFeedbackStub instead.

+
+  // Indicates that the connection supports video packet acknowledgments.
+  virtual bool SupportsAcks() { return false; }
 
  protected:
   VideoStub() {}