Remove the dependency of TransportChannel and TransportChannelImpl.

webrtc/media/sctp/sctptransport.cc

Index: webrtc/media/sctp/sctptransport.cc
diff --git a/webrtc/media/sctp/sctptransport.cc b/webrtc/media/sctp/sctptransport.cc
index b95cf8a4baf444bc3f14aee79e47e9a9e2983d0a..b766d75f75f1b6a26811fec7f5b7fa307253d603 100644
--- a/webrtc/media/sctp/sctptransport.cc
+++ b/webrtc/media/sctp/sctptransport.cc
@@ -384,7 +384,7 @@ class SctpTransport::UsrSctpWrapper {
 };
 
 SctpTransport::SctpTransport(rtc::Thread* network_thread,
-                             TransportChannel* channel)
+                             DtlsTransportInternal* channel)
     : network_thread_(network_thread),
       transport_channel_(channel),
       was_ever_writable_(channel->writable()) {
@@ -399,7 +399,8 @@ SctpTransport::~SctpTransport() {
   CloseSctpSocket();
 }
 
-void SctpTransport::SetTransportChannel(cricket::TransportChannel* channel) {
+void SctpTransport::SetTransportChannel(
+    cricket::DtlsTransportInternal* channel) {
   RTC_DCHECK_RUN_ON(network_thread_);
   RTC_DCHECK(channel);
   DisconnectTransportChannelSignals();