Fix BaseChannel destructor when network thread differ from worker thread

BUG=webrtc:5645
R=pthatcher@webrtc.org

Review URL: https://codereview.webrtc.org/1970223002 .

Cr-Commit-Position: refs/heads/master@{#12740}
diff --git a/webrtc/pc/channel.h b/webrtc/pc/channel.h
index df75245..2f66f12 100644
--- a/webrtc/pc/channel.h
+++ b/webrtc/pc/channel.h
@@ -314,7 +314,8 @@
 
  private:
   bool InitNetwork_n();
-  void DeinitNetwork_n();
+  void DisconnectTransportChannels_n();
+  void DestroyTransportChannels_n();
   void SignalSentPacket_n(TransportChannel* channel,
                           const rtc::SentPacket& sent_packet);
   void SignalSentPacket_w(const rtc::SentPacket& sent_packet);