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

webrtc/sdk/android/src/jni/pc/rtpreceiverobserver_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/audio_jni.h"
+#include "webrtc/sdk/android/src/jni/pc/rtpreceiverobserver_jni.h"
 
-#include "webrtc/api/audio_codecs/builtin_audio_decoder_factory.h"
-#include "webrtc/api/audio_codecs/builtin_audio_encoder_factory.h"
+#include "webrtc/sdk/android/src/jni/pc/java_native_conversion.h"
 
 namespace webrtc_jni {
 
-rtc::scoped_refptr<webrtc::AudioDecoderFactory> CreateAudioDecoderFactory() {
-  return webrtc::CreateBuiltinAudioDecoderFactory();
-}
+void RtpReceiverObserverJni::OnFirstPacketReceived(
+    cricket::MediaType media_type) {
+  JNIEnv* const jni = AttachCurrentThreadIfNeeded();
 
-rtc::scoped_refptr<webrtc::AudioEncoderFactory> CreateAudioEncoderFactory() {
-  return webrtc::CreateBuiltinAudioEncoderFactory();
+  jmethodID j_on_first_packet_received_mid = GetMethodID(
+      jni, GetObjectClass(jni, *j_observer_global_), "onFirstPacketReceived",
+      "(Lorg/webrtc/MediaStreamTrack$MediaType;)V");
+  // Get the Java version of media type.
+  jobject JavaMediaType = NativeToJavaMediaType(jni, media_type);
+  // Trigger the callback function.
+  jni->CallVoidMethod(*j_observer_global_, j_on_first_packet_received_mid,
+                      JavaMediaType);
+  CHECK_EXCEPTION(jni) << "error during CallVoidMethod";
 }
 
 }  // namespace webrtc_jni