Fix WebRTC transport to use single offer-answer exchange instead of two.

remoting/host/client_session.h

Index: remoting/host/client_session.h
diff --git a/remoting/host/client_session.h b/remoting/host/client_session.h
index 0caf5e10ff326c5a96a646da80d90174ccfc2bef..63b36a5090a94d11eef7783a91dfc05ea1a55bee 100644
--- a/remoting/host/client_session.h
+++ b/remoting/host/client_session.h
@@ -44,13 +44,16 @@ class InputInjector;
 class MouseShapePump;
 class ScreenControls;
 
+namespace protocol {
+class VideoLayout;
+}  // namespace protocol
+
 // A ClientSession keeps a reference to a connection to a client, and maintains
 // per-client state.
-class ClientSession
-    : public base::NonThreadSafe,
-      public protocol::HostStub,
-      public protocol::ConnectionToClient::EventHandler,
-      public ClientSessionControl {
+class ClientSession : public base::NonThreadSafe,
+                      public protocol::HostStub,
+                      public protocol::ConnectionToClient::EventHandler,
+                      public ClientSessionControl {
  public:
   // Callback interface for passing events to the ChromotingHost.
   class EventHandler {
@@ -112,6 +115,7 @@ class ClientSession
       protocol::ConnectionToClient* connection) override;
   void OnConnectionAuthenticated(
       protocol::ConnectionToClient* connection) override;
+  void OnCreateVideoStreams(protocol::ConnectionToClient* connection) override;
   void OnConnectionChannelsConnected(
       protocol::ConnectionToClient* connection) override;
   void OnConnectionClosed(protocol::ConnectionToClient* connection,
@@ -226,6 +230,10 @@ class ClientSession
   bool lossless_video_encode_;
   bool lossless_video_color_;
 
+  // VideoLayout is sent only after the capabilities are negotiated with the
+  // client. Until then it's stored in |pending_video_layout_message_|.

[Jamie, 2016/04/04 18:21:47]

Maybe expand on this a bit to explain why the message can't be sent until then
(since it's not conditional on what the capabilities are). If you think that's
too much detail for the header, maybe move it to the implementation.

Is it a client-side limitation, and if so can it be fixed there?

[Sergey Ulanov, 2016/04/05 21:21:54]

My thinking was that in the future we may need to change the format of that
messages depending on the capabilities. But looking at this today, I don't think
we really need this right now, so I removed this requirement. In any case the
message can be sent only after control channel is connected, so we still need
this variable.
No, it's not client-side limitation.

+  scoped_ptr<protocol::VideoLayout> pending_video_layout_message_;
+
   // Used to disable callbacks to |this| once DisconnectSession() has been
   // called.
   base::WeakPtrFactory<ClientSessionControl> weak_factory_;