Make OS audio buffer size limits visible.

media/base/mac/audio_latency_mac.h

Index: media/base/mac/audio_latency_mac.h
diff --git a/media/base/mac/audio_latency_mac.h b/media/base/mac/audio_latency_mac.h
new file mode 100644
index 0000000000000000000000000000000000000000..e6ad4ef7f1a82006acf62766a44491dd742af6c0
--- /dev/null
+++ b/media/base/mac/audio_latency_mac.h
@@ -0,0 +1,18 @@
+// Copyright 2017 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.
+
+#ifndef MEDIA_BASE_MAC_AUDIO_LATENCY_MAC_H_
+#define MEDIA_BASE_MAC_AUDIO_LATENCY_MAC_H_
+
+#include "base/macros.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+MEDIA_EXPORT int GetMinAudioBufferSizeMacOS(int min_buffer_size,
+                                            int sample_rate);
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_MAC_AUDIO_LATENCY_MAC_H_