Adds media::AudioPullFifo class to Chrome.

media/base/audio_pull_fifo.cc

Index: media/base/audio_pull_fifo.cc
diff --git a/media/base/audio_pull_fifo.cc b/media/base/audio_pull_fifo.cc
new file mode 100644
index 0000000000000000000000000000000000000000..d28106a16884116789f039ee6798e274f9c6a267
--- /dev/null
+++ b/media/base/audio_pull_fifo.cc
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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.
+
+#include "media/base/audio_pull_fifo.h"
+
+#include "base/logging.h"
+
+namespace media {
+
+AudioPullFifo::AudioPullFifo(int channels, int frames,
+                             const ReadCB& read_cb, int read_frames)
+    : read_cb_(read_cb) {
+  DCHECK_LE(read_frames, frames);
+  audio_fifo_.reset(new AudioFifo(channels, frames));
+  audio_bus_ = AudioBus::Create(channels, read_frames);
+}
+
+AudioPullFifo::~AudioPullFifo() {
+  read_cb_.Reset();
+}
+
+void AudioPullFifo::Consume(AudioBus* destination, int frames_to_consume) {
+  DCHECK(destination);
+
+  if (frames_to_consume > audio_fifo_->frames()) {
+    // We don't have enough data in the FIFO to fulfill the request and must
+    // ask the provider for more data.
+    FillBuffer(frames_to_consume - audio_fifo_->frames());
+  }
+
+  // We are now able to copy the requested amount of data to the destination.
+  audio_fifo_->Consume(destination, frames_to_consume);
+}
+
+void AudioPullFifo::FillBuffer(int frames) {
+  // Keep asking the provider to give us data until we have received at least
+  // |frames| number of audio data. Push new data to the FIFO in segments with
+  // the same size as the audio bus (set by |read_frames| in the ctor).
+  int frames_provided = 0;
+  while (frames_provided < frames) {
+    // Read audio data from the provider asking for |read_frames|.
+    read_cb_.Run(audio_bus_.get());
+
+    // Add the acquired data to the FIFO.
+    audio_fifo_->Push(audio_bus_.get());
+
+    // Keep adding to the FIFO until we have added at least |frames| number
+    // of frames.
+    frames_provided += audio_bus_->frames();
+  }
+}
+
+}  // namespace media