device/bluetooth:Implement Register() for BluetoothAudioSinkChromeOS.

device/bluetooth/bluetooth_audio_sink.h

 // Copyright 2014 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 DEVICE_BLUETOOTH_BLUETOOTH_AUDIO_SINK_H_
 #define DEVICE_BLUETOOTH_BLUETOOTH_AUDIO_SINK_H_
 
 #include <stdint.h>
 #include <string>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
+#include "device/bluetooth/bluetooth_export.h"
 
 namespace device {
 
 // TODO(mcchou): Define a BluetoothAudioSink specific IOBuffer abstraction.
 
 // BluetoothAudioSink represents a local A2DP audio sink where a remote device
 // can stream audio data. Once a BluetoothAudioSink is successfully registered,
 // user applications can obtain a pointer to a BluetoothAudioSink object via
 // the interface provided by BluetoothAdapter. The validity of a
 // BluetoothAudioSink depends on whether BluetoothAdapter is present and whether
 // it is powered.
-class BluetoothAudioSink : public base::RefCounted<BluetoothAudioSink> {
+class DEVICE_BLUETOOTH_EXPORT BluetoothAudioSink
+    : public base::RefCounted<BluetoothAudioSink> {
  public:
   // Possible values indicating the connection states between the
   // BluetoothAudioSink and the remote device.
   enum State {
     STATE_INVALID,  // BluetoothAdapter not presented or not powered.
     STATE_DISCONNECTED,  // Not connected.
     STATE_IDLE,  // Connected but not streaming.
     STATE_PENDING,  // Connected, streaming but not acquired.
     STATE_ACTIVE,  // Connected, streaming and acquired.
   };
@@ skipping 54 matching lines @@
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
 
   // Getters for state and volume.
   virtual State GetState() const = 0;
   virtual uint16_t GetVolume() const = 0;
 
  protected:
   friend class base::RefCounted<BluetoothAudioSink>;
   BluetoothAudioSink();
+
+  // The destructor invokes Unregister() to ensure the audio sink will be
+  // unregistered even if the user applications fail to do so.
   virtual ~BluetoothAudioSink();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(BluetoothAudioSink);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_BLUETOOTH_BLUETOOTH_AUDIO_SINK_H_