Change default audio device from "plug:default" to "default".

media/audio/linux/alsa_output.h

Index: media/audio/linux/alsa_output.h
diff --git a/media/audio/linux/alsa_output.h b/media/audio/linux/alsa_output.h
index b6d405b3fd90dbd715a03fd16a3df2df147a3efe..42cd3c87ae268e0d383085608c7ae81269683a9c 100644
--- a/media/audio/linux/alsa_output.h
+++ b/media/audio/linux/alsa_output.h
@@ -43,8 +43,9 @@ class AlsaPCMOutputStream :
     public AudioOutputStream,
     public base::RefCountedThreadSafe<AlsaPCMOutputStream> {
  public:
-  // Set to "plug:default" which should allow ALSA to do whatever is
-  // necessary to simulate an audio device capable of handling our PCMs.
+  // Set to "default" which should avoid locking the sound device and allow
+  // ALSA to multiplex sound from different processes that want to write PCM
+  // data.
   static const char* kDefaultDevice;
 
   // Create a PCM Output stream for the ALSA device identified by