Relanding: Break peerconnection_jni.cc into multiple files, in "pc" directory.

webrtc/sdk/android/src/jni/pc/null_media_jni.cc

 /*
  *  Copyright 2017 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/sdk/android/src/jni/media_jni.h"
+#include "webrtc/sdk/android/src/jni/pc/media_jni.h"
 
 namespace webrtc_jni {
 
 webrtc::CallFactoryInterface* CreateCallFactory() {
   return nullptr;
 }
 
 webrtc::RtcEventLogFactoryInterface* CreateRtcEventLogFactory() {
   return nullptr;
 }
 
 cricket::MediaEngineInterface* CreateMediaEngine(
     webrtc::AudioDeviceModule* adm,
     const rtc::scoped_refptr<webrtc::AudioEncoderFactory>&
         audio_encoder_factory,
     const rtc::scoped_refptr<webrtc::AudioDecoderFactory>&
         audio_decoder_factory,
     cricket::WebRtcVideoEncoderFactory* video_encoder_factory,
     cricket::WebRtcVideoDecoderFactory* video_decoder_factory,
     rtc::scoped_refptr<webrtc::AudioMixer> audio_mixer) {
   return nullptr;
 }
 
 }  // namespace webrtc_jni