Abort expensive AudioManager methods once shutdown starts.

media/audio/audio_manager_base.h

Index: media/audio/audio_manager_base.h
diff --git a/media/audio/audio_manager_base.h b/media/audio/audio_manager_base.h
index 4c088fb54ffb6b9dff7a4768fb9069ca6cc1c5ac..22d5d497bc9ef38edf042bd027163a1d51369596 100644
--- a/media/audio/audio_manager_base.h
+++ b/media/audio/audio_manager_base.h
@@ -8,6 +8,7 @@
 #include <string>
 #include <utility>
 
+#include "base/atomic_ref_count.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/scoped_vector.h"
@@ -196,6 +197,9 @@ class MEDIA_EXPORT AudioManagerBase : public AudioManager {
   // Proxy for creating AudioLog objects.
   AudioLogFactory* const audio_log_factory_;
 
+  // Used to exit early from expensive methods after shutdown has started.
+  base::AtomicRefCount in_shutdown_;
+
   DISALLOW_COPY_AND_ASSIGN(AudioManagerBase);
 };