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..1c00f42f18c489cc62c549dc070dcf49baf61ee6 100644
--- a/remoting/host/client_session.cc
+++ b/remoting/host/client_session.cc
@@ -197,9 +197,12 @@ 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_);
+
+  if (pending_video_layout_message_) {
+    connection_->client_stub()->SetVideoLayout(*pending_video_layout_message_);
+    pending_video_layout_message_.reset();
+  }
 }
 
 void ClientSession::RequestPairing(
@@ -295,6 +298,26 @@ void ClientSession::OnConnectionAuthenticated(
   clipboard_echo_filter_.set_client_stub(connection_->client_stub());
 }
 
+void ClientSession::OnCreateVideoStreams(
+    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());
@@ -315,20 +338,6 @@ 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 =
@@ -448,7 +457,13 @@ 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 capabilities negotiation has finished.
+    if (client_capabilities_) {
+      connection_->client_stub()->SetVideoLayout(layout);
+    } else {
+      pending_video_layout_message_.reset(new protocol::VideoLayout(layout));
+    }
   }
 }