Remove the dependency of TransportChannel and TransportChannelImpl.

webrtc/p2p/base/udptransport.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.
  */
 
@@ skipping 28 matching lines @@
   UdpTransport(const std::string& transport_name,
                std::unique_ptr<rtc::AsyncPacketSocket> socket);
   ~UdpTransport();
 
   // Overrides of UdpTransportInterface, used by the API consumer.
   rtc::SocketAddress GetLocalAddress() const override;
   bool SetRemoteAddress(const rtc::SocketAddress& addr) override;
   rtc::SocketAddress GetRemoteAddress() const override;
 
   // Overrides of PacketTransportInterface, used by webrtc internally.
-  const std::string debug_name() const override { return transport_name_; }
+  std::string debug_name() const override { return transport_name_; }
 
   bool receiving() const override {
     // TODO(johan): Implement method and signal.
     return true;
   }
 
   bool writable() const override;
 
   int SendPacket(const char* data,
                  size_t len,
@@ skipping 16 matching lines @@
   std::string transport_name_;
   int send_error_ = 0;
   std::unique_ptr<rtc::AsyncPacketSocket> socket_;
   // If not set, will be an "nil" address ("IsNil" returns true).
   rtc::SocketAddress remote_address_;
   rtc::ThreadChecker network_thread_checker_;
 };
 }  // namespace cricket
 
 #endif  // WEBRTC_P2P_BASE_UDPTRANSPORT_H_