Make PacketTransportInternal inherit from PacketTransportInterface.

webrtc/p2p/base/packettransportinternal.h

Index: webrtc/p2p/base/packettransportinternal.h
diff --git a/webrtc/p2p/base/packettransportinternal.h b/webrtc/p2p/base/packettransportinternal.h
index 325c00e65c6aad2bc7c56e14910a77d3f703ef02..8e32f72480db17291d136c1779abf24b564047a4 100644
--- a/webrtc/p2p/base/packettransportinternal.h
+++ b/webrtc/p2p/base/packettransportinternal.h
@@ -15,6 +15,7 @@
 #include <vector>
 
 // This is included for PacketOptions.
+#include "webrtc/api/ortc/packettransportinterface.h"
 #include "webrtc/base/asyncpacketsocket.h"
 #include "webrtc/base/sigslot.h"
 #include "webrtc/base/socket.h"
@@ -28,7 +29,8 @@ struct PacketOptions;
 struct PacketTime;
 struct SentPacket;
 
-class PacketTransportInternal : public sigslot::has_slots<> {
+class PacketTransportInternal : public virtual webrtc::PacketTransportInterface,
+                                public sigslot::has_slots<> {
  public:
   // Identify the object for logging and debug purpose.
   virtual std::string debug_name() const = 0;
@@ -88,6 +90,9 @@ class PacketTransportInternal : public sigslot::has_slots<> {
   // Signalled each time a packet is sent on this channel.
   sigslot::signal2<PacketTransportInternal*, const rtc::SentPacket&>
       SignalSentPacket;
+
+ protected:
+  PacketTransportInternal* GetInternal() override { return this; }
 };
 
 }  // namespace rtc