(Relanding) 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..7ef006f14efdeed1dceefe1f80188702987d01be 100644
--- a/media/audio/mac/audio_auhal_mac.h
+++ b/media/audio/mac/audio_auhal_mac.h
@@ -88,6 +88,7 @@ class AUHALStream : public AudioOutputStream {
 
   AudioDeviceID device_id() const { return device_; }
   size_t requested_buffer_size() const { return number_of_frames_; }
+  AudioUnit audio_unit() const { return audio_unit_; }
 
  private:
   // AUHAL callback.
@@ -145,7 +146,9 @@ 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_;
 
   // Stores the number of frames that we actually get callbacks for.