Adds media::AudioPullFifo class to Chrome.

media/base/audio_pull_fifo.h

Index: media/base/audio_pull_fifo.h
diff --git a/media/base/audio_pull_fifo.h b/media/base/audio_pull_fifo.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.
+
+#ifndef MEDIA_BASE_AUDIO_PULL_FIFO_H_
+#define MEDIA_BASE_AUDIO_PULL_FIFO_H_
+
+#include "base/callback.h"
+#include "media/base/audio_fifo.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+// A FIFO (First In First Out) buffer to handle mismatches in buffer sizes
+// between a producer and consumer. The consumer will pull data from this FIFO.
+// If data is already available in the FIFO, it is provided to the consumer.
+// If insufficient data is available to satisfy the request, the FIFO will ask
+// the producer for more data to fulfill a request.
+class MEDIA_EXPORT AudioPullFifo {
+ public:
+  // Callback type for providing more data into the FIFO.  Expects AudioBus
+  // to be completely filled with data upon return; zero padded if not enough
+  // frames are available to satisfy the request.
+  typedef base::Callback<void(AudioBus* audio_bus)> ReadCB;
+
+  // Constructs an AudioPullFifo with the specified |read_cb|, which is used to
+  // read audio data to the FIFO if data is not already available. The internal
+  // FIFO can contain |channel| number of channels, where each channel is of
+  // length |frames| audio frames.
+  AudioPullFifo(int channels, int frames, const ReadCB& read_cb);
+  virtual ~AudioPullFifo();
+
+  // Consumes |frames_to_consume| audio frames from the FIFO and copies
+  // them to |destination|. If the FIFO does not have enough data, we ask
+  // the producer to give us more data to fulfill the request using the
+  // ReadCB implementation.
+  void Consume(AudioBus* destination, int frames_to_consume);
+
+  // Empties the FIFO without deallocating any memory.
+  void Clear();
+
+ private:
+  // Attempt to fulfill the request using what is available in the FIFO.
+  // Append new data to the |destination| starting at |write_pos|.
+  void ReadFromFifo(
+      AudioBus* destination, int* frames_to_provide, int* write_pos);
+
+  // Source of data to the FIFO.
+  ReadCB read_cb_;
+
+  // The actual FIFO.
+  scoped_ptr<AudioFifo> fifo_;
+
+  // Temporary audio bus to hold the data from the producer.
+  scoped_ptr<AudioBus> bus_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioPullFifo);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_AUDIO_PULL_FIFO_H_