Change the way we are stopping audio stream on Mac once again.

media/audio/mac/audio_output_mac.h

Index: media/audio/mac/audio_output_mac.h
===================================================================
--- media/audio/mac/audio_output_mac.h	(revision 142757)
+++ media/audio/mac/audio_output_mac.h	(working copy)
@@ -51,6 +51,11 @@
   // Check and move channels if surround sound layout needs adjusted.
   bool CheckForAdjustedLayout(Channels input_channel, Channels output_channel);
 
+  // Callback we are installing to find out when the stream is stopped.
+  static void IsRunningCallback(void* p_this,
+                                AudioQueueRef queue,
+                                AudioQueuePropertyID inID);
+
   // The OS calls back here when an audio buffer has been processed.
   static void RenderCallback(void* p_this, AudioQueueRef queue,
                              AudioQueueBufferRef buffer);
@@ -98,11 +103,13 @@
   bool should_down_mix_;
 
   // Event used for synchronization when stopping the stream.
-  // Callback sets it after stream is stopped.
+  // Callback sets it after stream is fully stopped.
   base::WaitableEvent stopped_event_;
-  // When stopping we keep track of number of buffers in flight and
-  // signal "stop completed" from the last buffer's callback.
-  int num_buffers_left_;
+  // Flag set by rendering callback when it asks OS to stop the stream.
+  // All subsequent renderer callbacks calls just exit immediately, they
+  // are called to release the buffer (and we do it when closing the stream,
+  // not in the callback).
+  bool stop_requested_;
 
   DISALLOW_COPY_AND_ASSIGN(PCMQueueOutAudioOutputStream);
 };