Add a block based Audio FIFO.

media/base/audio_fifo.h

Index: media/base/audio_fifo.h
diff --git a/media/base/audio_fifo.h b/media/base/audio_fifo.h
index c00dd40fef9c99b202e18c35cbce7d09b69e4eea..154fd315f483d39f44603aded84ec95d0899f200 100644
--- a/media/base/audio_fifo.h
+++ b/media/base/audio_fifo.h
@@ -21,6 +21,10 @@ class MEDIA_EXPORT AudioFifo {
   AudioFifo(int channels, int frames);
   virtual ~AudioFifo();
 
+  static void GetSizes(int pos, int max_size, int in_size, int* size,
+                       int* wrap_size);
+  static int UpdatePos(int pos, int step, int max_size);
+
   // Pushes all audio channel data from |source| to the FIFO.
   // Push() will crash if the allocated space is insufficient.
   void Push(const AudioBus* source);