Introduce rtc::PacketTransportInterface and let cricket::TransportChannel inherit.

webrtc/p2p/BUILD.gn

 # Copyright (c) 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.
 
 import("../build/webrtc.gni")
 
@@ skipping 18 matching lines @@
     "base/dtlstransport.h",
     "base/dtlstransportchannel.cc",
     "base/dtlstransportchannel.h",
     "base/p2pconstants.cc",
     "base/p2pconstants.h",
     "base/p2ptransport.cc",
     "base/p2ptransport.h",
     "base/p2ptransportchannel.cc",
     "base/p2ptransportchannel.h",
     "base/packetsocketfactory.h",
+    "base/packettransport.h",
     "base/port.cc",
     "base/port.h",
     "base/portallocator.cc",
     "base/portallocator.h",
     "base/portinterface.h",
     "base/pseudotcp.cc",
     "base/pseudotcp.h",
     "base/relayport.cc",
     "base/relayport.h",
     "base/session.cc",
@@ skipping 120 matching lines @@
       suppressed_configs += [ "//build/config/clang:find_bad_constructs" ]
     }
 
     deps = [
       ":libstunprober",
       ":rtc_p2p",
       "../system_wrappers:field_trial_default",
     ]
   }
 }