Safe and reliable fix for 2 race conditions.

content/renderer/media/audio_device.h

Index: content/renderer/media/audio_device.h
===================================================================
--- content/renderer/media/audio_device.h	(revision 116480)
+++ content/renderer/media/audio_device.h	(working copy)
@@ -101,7 +101,6 @@
               int channels,
               double sample_rate,
               RenderCallback* callback);
-  virtual ~AudioDevice();
 
   void Initialize(size_t buffer_size,
                   int channels,
@@ -178,6 +177,11 @@
     base::SyncSocket socket_;
   };
 
+  // Magic required by ref_counted.h to avoid any code deleting the object
+  // accidently while there are references to it.
+  friend class base::RefCountedThreadSafe<AudioDevice>;
+  virtual ~AudioDevice();
+
   // Methods called on IO thread ----------------------------------------------
   // The following methods are tasks posted on the IO thread that needs to
   // be executed on that thread. They interact with AudioMessageFilter and