Add OSX aggregate audio device support for best performance.

media/audio/mac/aggregate_device_manager.h

Index: media/audio/mac/aggregate_device_manager.h
===================================================================
--- media/audio/mac/aggregate_device_manager.h	(revision 0)
+++ media/audio/mac/aggregate_device_manager.h	(revision 0)
@@ -0,0 +1,62 @@
+// Copyright 2013 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_AUDIO_MAC_AGGREGATE_DEVICE_MANAGER_H_
+#define MEDIA_AUDIO_MAC_AGGREGATE_DEVICE_MANAGER_H_
+
+#include <CoreAudio/CoreAudio.h>
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+class MEDIA_EXPORT AggregateDeviceManager {
+ public:
+  AggregateDeviceManager();
+  ~AggregateDeviceManager();
+
+  // Returns |true| if the default input and output devices are suitable
+  // for use with an aggregate device.
+  bool UseDefaultAggregateDevice();

[no longer working on chromium, 2013/04/03 21:11:57]

can we merge this UseDefaultAggregateDevice to GetDefaultAggregateDevice?

[Chris Rogers, 2013/04/05 20:01:38]

Yes, good point.  DONE

+
+  // Lazily creates an aggregate device based on the default
+  // input and output devices.
+  AudioDeviceID GetDefaultAggregateDevice();
+
+ private:
+  // Helper methods.
+
+  // The caller is responsible for releasing the CFStringRef.
+  static CFStringRef GetDeviceUID(AudioDeviceID id);
+
+  static OSStatus GetDeviceName(AudioDeviceID id, char* name, UInt32 size);
+  static UInt32 GetClockDomain(AudioDeviceID device_id);
+  static OSStatus GetPluginID(AudioObjectID* id);
+
+  CFMutableDictionaryRef CreateAggregateDeviceDictionary(
+      AudioDeviceID input_id,
+      AudioDeviceID output_id);
+
+  CFMutableArrayRef CreateSubDeviceArray(CFStringRef input_device_UID,
+                                         CFStringRef output_device_UID);
+
+  OSStatus CreateAggregateDevice(AudioDeviceID input_id,
+                                 AudioDeviceID output_id,
+                                 AudioDeviceID* aggregate_device);
+  OSStatus DestroyAggregateDevice();
+
+  AudioObjectID plugin_id_;
+  AudioDeviceID input_device_;
+  AudioDeviceID output_device_;
+
+  AudioDeviceID aggregate_device_;
+
+  DISALLOW_COPY_AND_ASSIGN(AggregateDeviceManager);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_MAC_AGGREGATE_DEVICE_MANAGER_H_