Simple cleanups of AudioDecoder and AudioEncoder classes

webrtc/modules/audio_coding/codecs/ilbc/interface/audio_decoder_ilbc.h

 /*
  *  Copyright (c) 2015 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.
  */
 
 #ifndef WEBRTC_MODULES_AUDIO_CODING_CODECS_ILBC_INTERFACE_AUDIO_DECODER_ILBC_H_
 #define WEBRTC_MODULES_AUDIO_CODING_CODECS_ILBC_INTERFACE_AUDIO_DECODER_ILBC_H_
 
 #include "webrtc/modules/audio_coding/codecs/audio_decoder.h"
 
 typedef struct iLBC_decinst_t_ IlbcDecoderInstance;
 
 namespace webrtc {
 
-class AudioDecoderIlbc : public AudioDecoder {
+class AudioDecoderIlbc final : public AudioDecoder {
  public:
   AudioDecoderIlbc();
   ~AudioDecoderIlbc() override;
   bool HasDecodePlc() const override;
   size_t DecodePlc(size_t num_frames, int16_t* decoded) override;
   void Reset() override;
   size_t Channels() const override;
 
  protected:
   int DecodeInternal(const uint8_t* encoded,
                      size_t encoded_len,
                      int sample_rate_hz,
                      int16_t* decoded,
                      SpeechType* speech_type) override;
 
  private:
   IlbcDecoderInstance* dec_state_;
   RTC_DISALLOW_COPY_AND_ASSIGN(AudioDecoderIlbc);
 };
 
 }  // namespace webrtc
 #endif  // WEBRTC_MODULES_AUDIO_CODING_CODECS_ILBC_INTERFACE_AUDIO_DECODER_ILBC_H_