Add support for threadsafe completion callback factory.

ppapi/proxy/ppb_file_ref_proxy.h

Index: ppapi/proxy/ppb_file_ref_proxy.h
diff --git a/ppapi/proxy/ppb_file_ref_proxy.h b/ppapi/proxy/ppb_file_ref_proxy.h
index d15536e04b750b8b6e2e65dd8171deb0c840f162..64febfa1f20821d8335877ba846e754f0a2bf1d6 100644
--- a/ppapi/proxy/ppb_file_ref_proxy.h
+++ b/ppapi/proxy/ppb_file_ref_proxy.h
@@ -12,7 +12,7 @@
 #include "ppapi/c/pp_resource.h"
 #include "ppapi/c/pp_time.h"
 #include "ppapi/proxy/interface_proxy.h"
-#include "ppapi/proxy/proxy_non_thread_safe_ref_count.h"
+#include "ppapi/proxy/proxy_completion_callback_factory.h"
 #include "ppapi/utility/completion_callback_factory.h"
 
 namespace ppapi {
@@ -92,8 +92,7 @@ class PPB_FileRef_Proxy : public InterfaceProxy {
                                 const HostResource& host_resource,
                                 int callback_id);
 
-  pp::CompletionCallbackFactory<PPB_FileRef_Proxy,
-                                ProxyNonThreadSafeRefCount> callback_factory_;
+  ProxyCompletionCallbackFactory<PPB_FileRef_Proxy> callback_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PPB_FileRef_Proxy);
 };