Move AudioDecoder and related stuff to the api/ directory

webrtc/api/audio_codec/audio_format.h

 /*
  *  Copyright (c) 2016 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_AUDIO_FORMAT_H_
-#define WEBRTC_MODULES_AUDIO_CODING_CODECS_AUDIO_FORMAT_H_
+#ifndef WEBRTC_API_AUDIO_CODEC_AUDIO_FORMAT_H_
+#define WEBRTC_API_AUDIO_CODEC_AUDIO_FORMAT_H_
 
 #include <map>
 #include <ostream>
 #include <string>
 #include <utility>
 
 namespace webrtc {
 
 // SDP specification for a single audio codec.
 // NOTE: This class is still under development and may change without notice.
@@ skipping 32 matching lines @@
 std::ostream& operator<<(std::ostream& os, const SdpAudioFormat& saf);
 
 struct AudioCodecSpec {
   SdpAudioFormat format;
   bool allow_comfort_noise;  // This encoder can be used with an external
                              // comfort noise generator.
 };
 
 }  // namespace webrtc
 
-#endif  // WEBRTC_MODULES_AUDIO_CODING_CODECS_AUDIO_FORMAT_H_
+#endif  // WEBRTC_API_AUDIO_CODEC_AUDIO_FORMAT_H_