Restores larger output buffer size when output stream requiring smaller size is closed

media/audio/mac/audio_auhal_mac.h

Index: media/audio/mac/audio_auhal_mac.h
diff --git a/media/audio/mac/audio_auhal_mac.h b/media/audio/mac/audio_auhal_mac.h
index b4fce5d708e8b729a23ba7d11f2dd15efde8b432..feb6fff850d334ae4b10f1df97dae3093afc1e5a 100644
--- a/media/audio/mac/audio_auhal_mac.h
+++ b/media/audio/mac/audio_auhal_mac.h
@@ -24,6 +24,7 @@
 
 #include <memory>
 
+#include "base/atomicops.h"
 #include "base/cancelable_callback.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
@@ -88,6 +89,10 @@ class AUHALStream : public AudioOutputStream {
 
   AudioDeviceID device_id() const { return device_; }
   size_t requested_buffer_size() const { return number_of_frames_; }
+  size_t actual_buffer_size() const {
+    return base::subtle::Acquire_Load(&actual_io_buffer_frame_size_);
+  }
+  AudioUnit audio_unit() const { return audio_unit_; }
 
  private:
   // AUHAL callback.
@@ -145,9 +150,21 @@ class AUHALStream : public AudioOutputStream {
   // For convenience - same as in params_.
   const int output_channels_;
 
-  // Buffer-size.
+  // Size of audio buffer requested at construction. The actual buffer size
+  // is given by |actual_io_buffer_frame_size_| and it can differ from the
+  // requested size.
   const size_t number_of_frames_;
 
+  // Size of I/O buffers measured in number of audio frames. Default value is
+  // 512 but we always try to set it to a vaule as close as possible to
+  // |number_of_frames_|. It might not be possible to match the requested size,
+  // especially not if the utilized device is used by other streams as well.
+  // This value will be the same as |number_of_frames_requested_| but they are
+  // used for different purpuses and updated at different times.
+  // The member is read by the audio manager on the main browser thread
+  // (CrBrowserMain) and modified by this class on the Core Audio I/O thread.
+  base::subtle::Atomic32 actual_io_buffer_frame_size_;
+
   // Stores the number of frames that we actually get callbacks for.
   // This may be different from what we ask for, so we use this for stats in
   // order to understand how often this happens and what are the typical values.