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diff --git a/media/audio/audio_output_dispatcher_impl.h b/media/audio/audio_output_dispatcher_impl.h
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+// Copyright (c) 2012 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.
+
+// AudioOutputDispatcherImpl is an implementation of AudioOutputDispatcher.
+//
+// To avoid opening and closing audio devices more frequently than necessary,
+// each dispatcher has a pool of inactive physical streams. A stream is closed
+// only if it hasn't been used for a certain period of time (specified via the
+// constructor).
+//
+
+#ifndef MEDIA_AUDIO_AUDIO_OUTPUT_DISPATCHER_IMPL_H_
+#define MEDIA_AUDIO_AUDIO_OUTPUT_DISPATCHER_IMPL_H_
+
+#include <list>
+#include <map>
+
+#include "base/basictypes.h"
+#include "base/memory/ref_counted.h"
+#include "base/memory/weak_ptr.h"
+#include "base/timer.h"
+#include "media/audio/audio_io.h"
+#include "media/audio/audio_manager.h"
+#include "media/audio/audio_output_dispatcher.h"
+#include "media/audio/audio_parameters.h"
+
+class MessageLoop;
+
+namespace media {
+
+class AudioOutputProxy;
+
+class MEDIA_EXPORT AudioOutputDispatcherImpl : public AudioOutputDispatcher {
+ public:
+  // |close_delay_ms| specifies delay after the stream is paused until
+  // the audio device is closed.
+  AudioOutputDispatcherImpl(AudioManager* audio_manager,
+                            const AudioParameters& params,
+                            const base::TimeDelta& close_delay);
+
+  // Opens a new physical stream if there are no pending streams in
+  // |idle_streams_|.
+  virtual bool OpenStream() OVERRIDE;
+
+  // If there are pending streams in |idle_streams_| then it reuses one of
+  // them, otherwise creates a new one.
+  virtual bool StartStream(AudioOutputStream::AudioSourceCallback* callback,
+                           AudioOutputProxy* stream_proxy) OVERRIDE;
+
+  // Holds the physical stream temporarily in |pausing_streams_| and then
+  // |stream| is  added to the pool of pending streams (i.e. |idle_streams_|).
+  virtual void StopStream(AudioOutputProxy* stream_proxy) OVERRIDE;
+
+  virtual void StreamVolumeSet(AudioOutputProxy* stream_proxy,
+                               double volume) OVERRIDE;
+
+  virtual void CloseStream(AudioOutputProxy* stream_proxy) OVERRIDE;
+
+  virtual void Shutdown() OVERRIDE;
+
+ private:
+  typedef std::map<AudioOutputProxy*, AudioOutputStream*> AudioStreamMap;
+  friend class base::RefCountedThreadSafe<AudioOutputDispatcherImpl>;
+  virtual ~AudioOutputDispatcherImpl();
+
+  friend class AudioOutputProxyTest;
+
+  // Creates a new physical output stream, opens it and pushes to
+  // |idle_streams_|.  Returns false if the stream couldn't be created or
+  // opened.
+  bool CreateAndOpenStream();
+
+  // A task scheduled by StartStream(). Opens a new stream and puts
+  // it in |idle_streams_|.
+  void OpenTask();
+
+  // Before a stream is reused, it should sit idle for a bit.  This task is
+  // called once that time has elapsed.
+  void StopStreamTask();
+
+  // Called by |close_timer_|. Closes all pending streams.
+  void ClosePendingStreams();
+
+  base::TimeDelta pause_delay_;
+  size_t paused_proxies_;
+  typedef std::list<AudioOutputStream*> AudioOutputStreamList;
+  AudioOutputStreamList idle_streams_;
+  AudioOutputStreamList pausing_streams_;
+
+  // Used to post delayed tasks to ourselves that we cancel inside Shutdown().
+  base::WeakPtrFactory<AudioOutputDispatcherImpl> weak_this_;
+  base::DelayTimer<AudioOutputDispatcherImpl> close_timer_;
+
+  AudioStreamMap proxy_to_physical_map_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioOutputDispatcherImpl);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_AUDIO_OUTPUT_DISPATCHER_IMPL_H_