Create empty PayloadTypeMapper files and add them to builds.

webrtc/media/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/config/linux/pkg_config.gni")
 import("../build/webrtc.gni")
@@ skipping 74 matching lines @@
     "base/videocommon.h",
     "base/videoframe.cc",
     "base/videoframe.h",
     "base/videoframefactory.cc",
     "base/videoframefactory.h",
     "base/videorenderer.h",
     "base/videosourcebase.cc",
     "base/videosourcebase.h",
     "devices/videorendererfactory.h",
     "engine/nullwebrtcvideoengine.h",
+    "engine/payload_type_mapper.cc",
+    "engine/payload_type_mapper.h",
     "engine/simulcast.cc",
     "engine/simulcast.h",
     "engine/webrtccommon.h",
     "engine/webrtcmediaengine.cc",
     "engine/webrtcmediaengine.h",
     "engine/webrtcvideocapturer.cc",
     "engine/webrtcvideocapturer.h",
     "engine/webrtcvideocapturerfactory.cc",
     "engine/webrtcvideocapturerfactory.h",
     "engine/webrtcvideodecoderfactory.h",
@@ skipping 247 matching lines @@
     deps += [
       # TODO(kjellander): Move as part of work in bugs.webrtc.org/4243.
       ":rtc_media",
       ":rtc_unittest_main",
       "../audio",
       "../base:rtc_base_tests_utils",
       "../system_wrappers:metrics_default",
     ]
   }
 }