Eliminate channel.h from peer_connection.cc

This limits the exposure of the implementation of ChannelInterface.

Bug: webrtc:13931
Change-Id: Ifc0fa496c210413d81ad71f44fa4040b881d092c
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/260561
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36725}

pc/peer_connection.cc

diff --git a/pc/peer_connection.cc b/pc/peer_connection.cc
index f13d5a9..957c2ec 100644
--- a/pc/peer_connection.cc
+++ b/pc/peer_connection.cc
@@ -42,7 +42,6 @@
 #include "p2p/base/p2p_constants.h"
 #include "p2p/base/p2p_transport_channel.h"
 #include "p2p/base/transport_info.h"
-#include "pc/channel.h"
 #include "pc/ice_server_parsing.h"
 #include "pc/rtp_receiver.h"
 #include "pc/rtp_receiver_proxy.h"
@@ -1559,10 +1558,10 @@
       if (transceiver->media_type() != cricket::MEDIA_TYPE_VIDEO)
         continue;
 
-      auto* video_channel = static_cast<cricket::VideoChannel*>(
-          transceiver->internal()->channel());
+      auto* video_channel = transceiver->internal()->channel();
       if (video_channel)
-        channels.push_back(video_channel->media_channel());
+        channels.push_back(static_cast<cricket::VideoMediaChannel*>(
+            video_channel->media_channel()));
     }
 
     worker_thread()->Invoke<void>(