Replace AudioDecoderConfig with simple accessors on AudioDecoder.

media/base/audio_decoder_config.h

-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef MEDIA_BASE_AUDIO_DECODER_CONFIG_H_
-#define MEDIA_BASE_AUDIO_DECODER_CONFIG_H_
-
-#include "media/base/channel_layout.h"
-
-namespace media {
-
-struct AudioDecoderConfig {
-  AudioDecoderConfig(int bits, ChannelLayout layout, int rate)
-      : bits_per_channel(bits),
-        channel_layout(layout),
-        sample_rate(rate) {
-  }
-
-  int bits_per_channel;
-  ChannelLayout channel_layout;
-  int sample_rate;
-};
-
-}  // namespace media
-
-#endif  // MEDIA_BASE_AUDIO_DECODER_CONFIG_H_