Prepare for introduction of rtc::PacketTransportInterface.

A rtc::PacketTransportInterface typedef is introduced to allow preparing
downstream projects for the upcoming refactoring of
cricket::Transport. This refactoring will introduce
rtc::PacketTransportInterface in https://codereview.webrtc.org/2416023002/ .

BUG=webrtc:6531

Review-Url: https://codereview.webrtc.org/2429803002
Cr-Commit-Position: refs/heads/master@{#14672}

webrtc/p2p/BUILD.gn

@@ -36,6 +36,7 @@ rtc_static_library("rtc_p2p") {
     "base/p2ptransportchannel.cc",
     "base/p2ptransportchannel.h",
     "base/packetsocketfactory.h",
+    "base/packettransportinterface.h",
     "base/port.cc",
     "base/port.h",
     "base/portallocator.cc",

webrtc/p2p/base/packettransportinterface.h

@@ -0,0 +1,22 @@
+/*
+ *  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.
+ */
+
+#ifndef WEBRTC_P2P_BASE_PACKETTRANSPORTINTERFACE_H_
+#define WEBRTC_P2P_BASE_PACKETTRANSPORTINTERFACE_H_
+
+namespace cricket {
+class TransportChannel;
+}
+
+namespace rtc {
+typedef cricket::TransportChannel PacketTransportInterface;
+}
+
+#endif  // WEBRTC_P2P_BASE_PACKETTRANSPORTINTERFACE_H_

webrtc/p2p/p2p.gyp

@@ -32,6 +32,7 @@
         'base/p2ptransport.h',
         'base/p2ptransportchannel.cc',
         'base/p2ptransportchannel.h',
+        'base/packettransportinterface.h',
         'base/packetsocketfactory.h',
         'base/port.cc',
         'base/port.h',