Refactor of Authenticator to allow it to ProcessMessage asynchronously and then call a callback

remoting/protocol/session.h

Index: remoting/protocol/session.h
diff --git a/remoting/protocol/session.h b/remoting/protocol/session.h
index daa12e478c6f6e9261877b44f7a151f4d4872031..a542283001e6ced5fbb0359d11895c9a2442d9cd 100644
--- a/remoting/protocol/session.h
+++ b/remoting/protocol/session.h
@@ -29,11 +29,12 @@ class Session {
     // Created, but not connecting yet.
     INITIALIZING,
 
-    // Sent or received session-initiate, but haven't sent or received
-    // session-accept.
-    // TODO(sergeyu): Do we really need this state?
+    // Sent session-initiate, but haven't received session-accept.
     CONNECTING,
 
+    // Received session-initiate, but haven't sent session-accept.
+    ACCEPTING,
+
     // Session has been accepted and is pending authentication.
     CONNECTED,