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..b1622e0c4110740605d1dd81a5ce8f11f0999aef
--- /dev/null
+++ b/media/base/audio_pull_fifo.cc
@@ -0,0 +1,59 @@
+// 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 <algorithm>
+
+#include "base/logging.h"
+
+namespace media {
+
+AudioPullFifo::AudioPullFifo(int channels, int frames, const ReadCB& read_cb)
+    : read_cb_(read_cb) {
+  fifo_.reset(new AudioFifo(channels, frames));
+  bus_ = AudioBus::Create(channels, frames);
+}
+
+AudioPullFifo::~AudioPullFifo() {
+  read_cb_.Reset();
+}
+
+void AudioPullFifo::Consume(AudioBus* destination, int frames_to_consume) {
+  DCHECK(destination);
+  DCHECK_LE(frames_to_consume, destination->frames());
+
+  int write_pos = 0;
+  int remaining_frames_to_provide = frames_to_consume;
+
+  // Try to fulfill the request using what's available in the FIFO.
+  ReadFromFifo(destination, &remaining_frames_to_provide, &write_pos);
+
+  // Get the remaining audio frames from the producer using the callback.
+  while (remaining_frames_to_provide > 0) {
+    // Fill up the FIFO by acquiring audio data from the producer.
+    read_cb_.Run(bus_.get());
+    fifo_->Push(bus_.get());
+
+    // Try to fulfill the request using what's available in the FIFO.
+    ReadFromFifo(destination, &remaining_frames_to_provide, &write_pos);
+  }
+}
+
+void AudioPullFifo::Clear() {
+  fifo_->Clear();
+}
+
+void AudioPullFifo::ReadFromFifo(AudioBus* destination,
+                                 int* frames_to_provide,
+                                 int* write_pos) {
+  DCHECK(frames_to_provide);
+  DCHECK(write_pos);
+  int frames = std::min(fifo_->frames(), *frames_to_provide);
+  fifo_->Consume(destination, *write_pos, frames);
+  *write_pos += frames;
+  *frames_to_provide -= frames;
+}
+
+}  // namespace media