Share one thread between all AudioOutputControllers instead of creating one per stream.

media/audio/mac/audio_manager_mac.h

Index: media/audio/mac/audio_manager_mac.h
diff --git a/media/audio/mac/audio_manager_mac.h b/media/audio/mac/audio_manager_mac.h
index c05e092812af6a6b9dcf049485046c0d22242ca1..fa25ece914ea3ed954c6f788778f209803b32fe0 100644
--- a/media/audio/mac/audio_manager_mac.h
+++ b/media/audio/mac/audio_manager_mac.h
@@ -6,14 +6,14 @@
 #define MEDIA_AUDIO_MAC_AUDIO_MANAGER_MAC_H_
 
 #include "base/basictypes.h"
-#include "media/audio/audio_io.h"
+#include "media/audio/audio_manager_base.h"
 
 class PCMQueueOutAudioOutputStream;
 
 // Mac OS X implementation of the AudioManager singleton. This class is internal
 // to the audio output and only internal users can call methods not exposed by
 // the AudioManager class.
-class AudioManagerMac : public AudioManager {
+class AudioManagerMac : public AudioManagerBase {
  public:
   AudioManagerMac() {};