Add GetSctpStats to PeerConnectionInternal, remove sctp_data_channels()

This removes code from DataChannelController that exposes
an internal vector of data channels and puts the onus of
returning stats for a data channel, on the data channel
object itself. This will come in handy as we make threading
changes to the data channel object.

Change-Id: Ie164cc5823cd5f9782fc5c9a63aa4c76b8229639
Bug: webrtc:11547, webrtc:11687
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/177244
Commit-Queue: Tommi <tommi@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31533}

pc/data_channel_controller.h

diff --git a/pc/data_channel_controller.h b/pc/data_channel_controller.h
index 156bbe5..c3e64ab 100644
--- a/pc/data_channel_controller.h
+++ b/pc/data_channel_controller.h
@@ -64,6 +64,9 @@
   void OnTransportChanged(
       DataChannelTransportInterface* data_channel_transport);
 
+  // Called from PeerConnection::GetDataChannelStats on the signaling thread.
+  std::vector<DataChannel::Stats> GetDataChannelStats() const;
+
   // Creates channel and adds it to the collection of DataChannels that will
   // be offered in a SessionDescription.
   rtc::scoped_refptr<DataChannel> InternalCreateDataChannel(
@@ -101,8 +104,6 @@
   void set_data_channel_transport(DataChannelTransportInterface* transport);
   const std::map<std::string, rtc::scoped_refptr<DataChannel>>*
   rtp_data_channels() const;
-  const std::vector<rtc::scoped_refptr<DataChannel>>* sctp_data_channels()
-      const;
 
   sigslot::signal1<DataChannel*>& SignalDataChannelCreated() {
     RTC_DCHECK_RUN_ON(signaling_thread());
@@ -137,6 +138,10 @@
                            const rtc::CopyOnWriteBuffer& payload,
                            cricket::SendDataResult* result);
 
+  // Called when all data channels need to be notified of a transport channel
+  // (calls OnTransportChannelCreated on the signaling thread).
+  void NotifyDataChannelsOfTransportCreated();
+
   rtc::Thread* network_thread() const;
   rtc::Thread* signaling_thread() const;