Android: Replace webrtc_jni namespace with nested jni namespace

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/pc/rtpreceiverobserver_jni.h"
 
 #include "webrtc/sdk/android/src/jni/pc/java_native_conversion.h"
 
-namespace webrtc_jni {
+namespace webrtc {
+namespace jni {
 
 void RtpReceiverObserverJni::OnFirstPacketReceived(
     cricket::MediaType media_type) {
   JNIEnv* const jni = AttachCurrentThreadIfNeeded();
 
   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
+}  // namespace jni
+}  // namespace webrtc