[chrome.displaySource] Add a base class for audio encoders.

extensions/renderer/api/display_source/wifi_display/wifi_display_audio_encoder.h

+// Copyright 2016 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 EXTENSIONS_RENDERER_API_DISPLAY_SOURCE_WIFI_DISPLAY_WIFI_DISPLAY_AUDIO_ENCODER_H_
+#define EXTENSIONS_RENDERER_API_DISPLAY_SOURCE_WIFI_DISPLAY_WIFI_DISPLAY_AUDIO_ENCODER_H_
+
+#include "content/public/renderer/media_stream_audio_sink.h"
+#include "extensions/renderer/api/display_source/wifi_display/wifi_display_media_encoder.h"
+#include "third_party/wds/src/libwds/public/audio_codec.h"
+
+namespace extensions {
+
+// This interface is a base class for audio used by the Wi-Fi Display media
+// pipeline.
+// Threading: the client code should belong to a single thread.
+class WiFiDisplayAudioEncoder : public WiFiDisplayMediaEncoder,
+                                public content::MediaStreamAudioSink {
+ public:
+  using AudioEncoderCallback =
+      base::Callback<void(scoped_refptr<WiFiDisplayAudioEncoder>)>;
+
+  static void Create(const wds::AudioCodec& audio_codec,
+                     const AudioEncoderCallback& encoder_callback);
+
+ protected:
+  explicit WiFiDisplayAudioEncoder(const wds::AudioCodec& audio_codec);
+  ~WiFiDisplayAudioEncoder() override;
+
+  size_t GetAudioCodecMode() const;
+
+  const wds::AudioCodec audio_codec_;
+};
+
+}  // namespace extensions
+
+#endif  // EXTENSIONS_RENDERER_API_DISPLAY_SOURCE_WIFI_DISPLAY_WIFI_DISPLAY_AUDIO_ENCODER_H_