Bug 1144984 - add missing includes in MediaTimer.cpp. r=bobbyholley

dom/media/MediaTimer.cpp

@@ -10,6 +10,8 @@
 
 #include "nsComponentManagerUtils.h"
 #include "nsThreadUtils.h"
+#include "mozilla/RefPtr.h"
+#include "SharedThreadPool.h"
 
 namespace mozilla {