Modified PeerConnection and WebRtcSession for end-to-end QuicDataChannel usage.

webrtc/api/quicdatachannel.cc

Index: webrtc/api/quicdatachannel.cc
diff --git a/webrtc/api/quicdatachannel.cc b/webrtc/api/quicdatachannel.cc
index 5493382e1a022650b997d678a7742b24b6fc14be..23f126e2c02d234ac3264088be150e4cd0d9131d 100644
--- a/webrtc/api/quicdatachannel.cc
+++ b/webrtc/api/quicdatachannel.cc
@@ -228,15 +228,18 @@ bool QuicDataChannel::SetTransportChannel(
     LOG(LS_ERROR) << "|channel| is NULL. Cannot set transport channel.";
     return false;
   }
-  if (quic_transport_channel_) {
-    if (channel == quic_transport_channel_) {
-      LOG(LS_WARNING) << "Ignoring duplicate transport channel.";
-      return true;
-    }
-    LOG(LS_ERROR) << "|channel| does not match existing transport channel.";
-    return false;
+
+  if (channel == quic_transport_channel_) {
+    LOG(LS_WARNING) << "Ignoring duplicate transport channel.";
+    return true;
   }
 
+  // Disconnect from the old transport channel.
+  if (quic_transport_channel_) {
+    quic_transport_channel_->SignalReadyToSend.disconnect(this);
+    quic_transport_channel_->SignalClosed.disconnect(this);
+  }
+  // Set new transport channel.

[Taylor Brandstetter, 2016/07/21 23:39:57]

Is it possible to switch transports in the middle of a session? Couldn't that
cause packets to be lost, since we're losing the state of the streams in the old
transport?

[pthatcher1, 2016/07/22 17:57:57]

We should at least do this:
 
if (state_ == kOpen) {
  return false;
}


Otherwise, I think changing the transport channel will work.

[Taylor Brandstetter, 2016/07/22 19:04:56]

If we base the success of "Set___Description" on the open state of the data
channel, that seems like it's asking for trouble. Sometimes it will succeed and
sometimes it won't depending on timing. I'd prefer to just always disallow it,
and tell people to use max-bundle or force bundling on the data transport.

[Zhi Huang, 2016/07/25 23:40:36]

I will revert this change for now. I think we might need this when negotiation.
But that comes later.

   quic_transport_channel_ = channel;
   LOG(LS_INFO) << "Setting QuicTransportChannel for QUIC data channel " << id_;
   DataState data_channel_state = worker_thread_->Invoke<DataState>(