Prepare for introduction of rtc::PacketTransportInterface.

webrtc/p2p/base/packettransportinterface.h

 /*
  *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#include "webrtc/base/optional.h"
+#ifndef WEBRTC_P2P_BASE_PACKETTRANSPORTINTERFACE_H_
+#define WEBRTC_P2P_BASE_PACKETTRANSPORTINTERFACE_H_
+
+namespace cricket {
+class TransportChannel;
+}
 
 namespace rtc {
-namespace optional_internal {
+typedef cricket::TransportChannel PacketTransportInterface;
+}
 
-#if RTC_HAS_ASAN
-
-void* FunctionThatDoesNothingImpl(void* x) { return x; }
-
-#endif
-
-}  // namespace optional_internal
-}  // namespace rtc
+#endif  // WEBRTC_P2P_BASE_PACKETTRANSPORTINTERFACE_H_