Android: Replace webrtc_jni namespace with nested jni namespace

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

 /*
  *  Copyright (c) 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/video_jni.h"
 
-namespace webrtc_jni {
+namespace webrtc {
+namespace jni {
 
 cricket::WebRtcVideoEncoderFactory* CreateVideoEncoderFactory(
     JNIEnv* jni,
     jobject j_encoder_factory) {
   return nullptr;
 }
 
 cricket::WebRtcVideoDecoderFactory* CreateVideoDecoderFactory(
     JNIEnv* jni,
     jobject j_decoder_factory) {
   return nullptr;
 }
 
 jobject GetJavaSurfaceTextureHelper(
     const rtc::scoped_refptr<SurfaceTextureHelper>& surface_texture_helper) {
   return nullptr;
 }
 
-}  // namespace webrtc_jni
+}  // namespace jni
+}  // namespace webrtc