Simplify AlsaPcmOutputStream and AudioManagerLinux. Code was thread-safe, but now

media/audio/linux/audio_manager_linux.h

Index: media/audio/linux/audio_manager_linux.h
===================================================================
--- media/audio/linux/audio_manager_linux.h	(revision 87982)
+++ media/audio/linux/audio_manager_linux.h	(working copy)
@@ -5,11 +5,9 @@
 #ifndef MEDIA_AUDIO_LINUX_AUDIO_MANAGER_LINUX_H_
 #define MEDIA_AUDIO_LINUX_AUDIO_MANAGER_LINUX_H_
 
-#include <map>
+#include <set>
 
 #include "base/memory/ref_counted.h"
-#include "base/memory/scoped_ptr.h"
-#include "base/synchronization/lock.h"
 #include "base/threading/thread.h"
 #include "media/audio/audio_manager_base.h"
 
@@ -46,9 +44,7 @@
 
   scoped_ptr<AlsaWrapper> wrapper_;
 
-  base::Lock lock_;
-  std::map<AlsaPcmOutputStream*, scoped_refptr<AlsaPcmOutputStream> >
-      active_streams_;
+  std::set<AlsaPcmOutputStream*> active_streams_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioManagerLinux);
 };