Implements AudioMessageFilter as member in RenderThread

base/memory/singleton.h

Index: base/memory/singleton.h
===================================================================
--- base/memory/singleton.h	(revision 89645)
+++ base/memory/singleton.h	(working copy)
@@ -109,6 +109,30 @@
   static base::subtle::Atomic32 dead_;
 };
 
+// Alternate traits for use with the Singleton<Type>.  Identical to
+// DefaultSingletonTraits except that AddRef() will be called on the singleton
+// upon construction and Release() will be called instead of delete when
+// the singleton is destructed.
+template<typename Type>
+struct RefCountedSingletonTraits {
+  // Allocates the reference counted object.
+  static Type* New() {
+    DCHECK(Type::ImplementsThreadSafeReferenceCounting());
+    Type* ptr = new Type();
+    ptr->AddRef();
+    return ptr;
+  }
+
+  // Destroys the reference counted object.
+  static void Delete(Type* x) {
+    DCHECK(Type::ImplementsThreadSafeReferenceCounting());
+    x->Release();
+  }
+
+  static const bool kRegisterAtExit = true;
+  static const bool kAllowedToAccessOnNonjoinableThread = false;
+};
+
 template <typename Type> intptr_t
     StaticMemorySingletonTraits<Type>::buffer_[kBufferSize];
 template <typename Type> base::subtle::Atomic32