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

remoting/host/client_session.cc

Index: remoting/host/client_session.cc
diff --git a/remoting/host/client_session.cc b/remoting/host/client_session.cc
index e3a6766e93b3e29d0e4653d01eb6a8440f2af1e2..e42a56ac2cd512a7a560720bd42260df84785dea 100644
--- a/remoting/host/client_session.cc
+++ b/remoting/host/client_session.cc
@@ -79,9 +79,6 @@ ClientSession::ClientSession(
       max_duration_(max_duration),
       audio_task_runner_(audio_task_runner),
       pairing_registry_(pairing_registry),
-      is_authenticated_(false),
-      pause_video_(false),
-      lossless_video_encode_(false),
       // Note that |lossless_video_color_| defaults to true, but actually only
       // controls VP9 video stream color quality.
       lossless_video_color_(!base::CommandLine::ForCurrentProcess()->HasSwitch(
@@ -197,8 +194,6 @@ void ClientSession::SetCapabilities(
 
   VLOG(1) << "Client capabilities: " << *client_capabilities_;
 
-  // Calculate the set of capabilities enabled by both client and host and
-  // pass it to the desktop environment if it is available.
   desktop_environment_->SetCapabilities(capabilities_);
 }
 
@@ -295,11 +290,34 @@ void ClientSession::OnConnectionAuthenticated(
   clipboard_echo_filter_.set_client_stub(connection_->client_stub());
 }
 
+void ClientSession::CreateVideoStreams(
+    protocol::ConnectionToClient* connection) {
+  DCHECK(CalledOnValidThread());
+  DCHECK_EQ(connection_.get(), connection);
+
+  // Create a VideoStream to pump frames from the capturer to the client.
+  video_stream_ = connection_->StartVideoStream(
+      desktop_environment_->CreateVideoCapturer());
+
+  video_stream_->SetSizeCallback(
+      base::Bind(&ClientSession::OnScreenSizeChanged, base::Unretained(this)));
+
+  // Apply video-control parameters to the new stream.
+  video_stream_->SetLosslessEncode(lossless_video_encode_);
+  video_stream_->SetLosslessColor(lossless_video_color_);
+
+  // Pause capturing if necessary.
+  video_stream_->Pause(pause_video_);
+}
+
 void ClientSession::OnConnectionChannelsConnected(
     protocol::ConnectionToClient* connection) {
   DCHECK(CalledOnValidThread());
   DCHECK_EQ(connection_.get(), connection);
 
+  DCHECK(!channels_connected_);
+  channels_connected_ = true;
+
   // Negotiate capabilities with the client.
   VLOG(1) << "Host capabilities: " << host_capabilities_;
   protocol::Capabilities capabilities;
@@ -315,20 +333,6 @@ void ClientSession::OnConnectionChannelsConnected(
       new MouseShapePump(desktop_environment_->CreateMouseCursorMonitor(),
                          connection_->client_stub()));
 
-  // Create a VideoStream to pump frames from the capturer to the client.
-  video_stream_ = connection_->StartVideoStream(
-      desktop_environment_->CreateVideoCapturer());
-
-  video_stream_->SetSizeCallback(
-      base::Bind(&ClientSession::OnScreenSizeChanged, base::Unretained(this)));
-
-  // Apply video-control parameters to the new stream.
-  video_stream_->SetLosslessEncode(lossless_video_encode_);
-  video_stream_->SetLosslessColor(lossless_video_color_);
-
-  // Pause capturing if necessary.
-  video_stream_->Pause(pause_video_);
-
   // Create an AudioPump if audio is enabled, to pump audio samples.
   if (connection_->session()->config().is_audio_enabled()) {
     scoped_ptr<AudioEncoder> audio_encoder =
@@ -338,6 +342,11 @@ void ClientSession::OnConnectionChannelsConnected(
         std::move(audio_encoder), connection_->audio_stub()));
   }
 
+  if (pending_video_layout_message_) {
+    connection_->client_stub()->SetVideoLayout(*pending_video_layout_message_);
+    pending_video_layout_message_.reset();
+  }
+
   // Notify the event handler that all our channels are now connected.
   event_handler_->OnSessionChannelsConnected(this);
 }
@@ -448,7 +457,14 @@ void ClientSession::OnScreenSizeChanged(const webrtc::DesktopSize& size,
     video_track->set_height(size.height() * kDefaultDpi / dpi.y());
     video_track->set_x_dpi(dpi.x());
     video_track->set_y_dpi(dpi.y());
-    connection_->client_stub()->SetVideoLayout(layout);
+
+    // VideoLayout can be sent only after the control channel is connected. This
+    // is necessary for the case in the future.

[Jamie, 2016/04/05 21:46:35]

I don't understand this second sentence. Are you saying that a future update
will make use of the VideoLayout message or that a future update will restrict
it to be sent only when the control channel is connected? Either way, I don't
think you need the second sentence, but feel free to clarify if you meant
something else.

[Sergey Ulanov, 2016/04/06 21:23:50]

I don't understand it either :-/. Removed.

+    if (channels_connected_) {
+      connection_->client_stub()->SetVideoLayout(layout);
+    } else {
+      pending_video_layout_message_.reset(new protocol::VideoLayout(layout));
+    }
   }
 }