Move AudioDecoder and related stuff to the api/ directory

BUG=webrtc:5805, webrtc:6725

Review-Url: https://codereview.webrtc.org/2668523004
Cr-Commit-Position: refs/heads/master@{#16534}

webrtc/api/audio_codecs/audio_decoder_factory.h

@@ -0,0 +1,37 @@
+/*
+ *  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_API_AUDIO_CODECS_AUDIO_DECODER_FACTORY_H_
+#define WEBRTC_API_AUDIO_CODECS_AUDIO_DECODER_FACTORY_H_
+
+#include <memory>
+#include <vector>
+
+#include "webrtc/api/audio_codecs/audio_decoder.h"
+#include "webrtc/api/audio_codecs/audio_format.h"
+#include "webrtc/base/refcount.h"
+
+namespace webrtc {
+
+// A factory that creates AudioDecoders.
+// NOTE: This class is still under development and may change without notice.
+class AudioDecoderFactory : public rtc::RefCountInterface {
+ public:
+  virtual std::vector<AudioCodecSpec> GetSupportedDecoders() = 0;
+
+  virtual bool IsSupportedDecoder(const SdpAudioFormat& format) = 0;
+
+  virtual std::unique_ptr<AudioDecoder> MakeAudioDecoder(
+      const SdpAudioFormat& format) = 0;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_API_AUDIO_CODECS_AUDIO_DECODER_FACTORY_H_