Let receiving() and SignalReceivingState be part of rtc::PacketTransportInterface.

webrtc/p2p/base/dtlstransportchannel.h

Index: webrtc/p2p/base/dtlstransportchannel.h
diff --git a/webrtc/p2p/base/dtlstransportchannel.h b/webrtc/p2p/base/dtlstransportchannel.h
index aac89c9f9fbe13533bfb4a93e7e9396e2f7f3a0f..5850813fcd6002d36b556572b31e9e1ead0b765d 100644
--- a/webrtc/p2p/base/dtlstransportchannel.h
+++ b/webrtc/p2p/base/dtlstransportchannel.h
@@ -216,7 +216,7 @@ class DtlsTransportChannelWrapper : public TransportChannelImpl {
   void OnSentPacket(rtc::PacketTransportInterface* transport,
                     const rtc::SentPacket& sent_packet);
   void OnReadyToSend(rtc::PacketTransportInterface* transport);
-  void OnReceivingState(TransportChannel* channel);
+  void OnReceivingState(rtc::PacketTransportInterface* transport);
   void OnDtlsEvent(rtc::StreamInterface* stream_, int sig, int err);
   bool SetupDtls();
   void MaybeStartDtls();