Implement video frame acknowledgements in the chromoting protocol.

remoting/protocol/protocol_mock_objects.cc

Index: remoting/protocol/protocol_mock_objects.cc
diff --git a/remoting/protocol/protocol_mock_objects.cc b/remoting/protocol/protocol_mock_objects.cc
index 7b51fe25310b239aa8cf43ba8b69a893c0c29242..90876360ca30e8c45c6959bf46ef991931c39db4 100644
--- a/remoting/protocol/protocol_mock_objects.cc
+++ b/remoting/protocol/protocol_mock_objects.cc
@@ -15,7 +15,8 @@ MockConnectionToClient::MockConnectionToClient(Session* session,
     : ConnectionToClient(session),
       clipboard_stub_(nullptr),
       host_stub_(host_stub),
-      input_stub_(nullptr) {
+      input_stub_(nullptr),
+      video_feedback_stub_(nullptr) {
 }
 
 MockConnectionToClient::~MockConnectionToClient() {}